# How to find the temperature of a planet accounting for the atmosphere?

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Recently, I started writing a program to generate star systems, and I need a formula to find the approximate surface temperature of a planet. I know of several formulas for this, for example this one based on the formula for equilibrium temperature I found from a site called burro.case.edu:

$$T_{P}=(T_{odot})(({1-a})^{1/4})left( sqrt{frac{R_{odot}}{2D}} ight)$$ Where $$T_{odot}$$ denotes the parent star's temperature in Kelvin, $$a$$ denotes the dimensionless bond albedo, $${R_{odot}}$$ denotes the parent star's radius in AU (not kilometers/solar radii), $$D$$ denotes the semi-major axis in AU, and $$T_{P}$$ denotes the resulting computed planet temperate in Kelvin.

For example, if we plug in the relevant numbers to Mars ($$T_{odot}=5778,a=0.25,R_{odot}=0.0046547454,D=1.524$$), we get an estimated temperature of Mars as 210.127 K, which is nearly spot-on with Mars's real temperature of 210 K. But if I plug in the formula for Venus, it gives a wildly off answer of about 260 K. In fact, this is briefly mentioned on the linked page:

Let's try this for Venus. Putting in the numbers (a=0.6, Tsun=5770K, Rsun=7x105 km, D=0.72 AU) we get the equilibrium temperature of Venus = 260 K. The surface temperature of Venus = 740 K. Whoa! Where'd we mess up?? For that matter, the equilibrium temperature of the Earth is 255 K (or ~ -1 F). Something's wrong!

Obviously this happens becausing trying to estimate a true temperature from the equilibrium temperature results in ignorance of the atmospheric pressure. Venus's atmosphere is about 93 atm, resulting in a runaway greenhouse effect and heating the temperature. On a smaller scale, the same thing occurs for Earth as it has a pressure of 1 atm. The temperature calculation for Mars worked well because it has a pressure of only 0.01 atm making the difference minimal.

So I started searching on the web for other sources which have bias terms accounting for the atmosphere, but I still can't find anything. All I currently have is a very rough approximation based on this Youtube video:

$$T_{P} = 255(frac{L^{1/4}}{sqrt{D}})+50sqrt{P}-50a$$

Where $$L$$ denotes the star's luminosity with respect to the Sun, $$P$$ denotes the planet's atmospheric pressure with respect to Earth, and all the other variables are the same as they were in the last approximation. But this is still far from perfect, Venus's temperature has a ~15 K deviation from the real temperature. So, is there any more accurate formula for the atmospheric temperature of a planet?

## Astronomers Have Found the Perfect Exoplanet to Study Another World’s Atmosphere

TESS (Transiting Exoplanet Survey Satellite) has found a new planet, and the discovery of this sub-Neptune exoplanet has scientists excited about atmospheres. The combination of the planet’s size, its thick atmosphere, and its orbit around a small M-class star close to Earth provides researchers with an opportunity to learn more about exoplanet atmospheres. We’re getting better and better at finding exoplanets, and studying their atmospheres is the next step in understanding them as a whole.

All of our exoplanet-detection strategies have an observation bias. It seems impossible to avoid. Even TESS (Transiting Exoplanet Survey Satellite), probably our most adept planet-finder, has an observation bias. Its predecessor Kepler was biased towards larger planets, and TESS doesn’t share that bias. But TESS still has a sort of blind spot due to how it operates.

No telescope can look everywhere at once, and TESS is no exception. It observes the sky mostly in 28-day chunks. So for one of those chunks, it focuses on one area for 28 days. To be confirmed as an exoplanet, an object must pass in front of its star twice in that 28 days. The end result of all this is that most of the planets TESS finds have orbital periods of less than 14 days.

Most of TESS’s observing is done in 28 day chunk, as the image shows. Image Credit: NASA/JPL

But this new planet, named TOI-1231 b, has a 24-day orbital period. This makes it a great target for the study of exoplanet atmospheres because it’s in front of its star longer and can be more easily studied. Universe Today readers know that studying light as it interacts with things is how we gain most of our knowledge about space. TESS itself won’t study the planet. Other missions like the James Webb Space Telescope (JWST) will take care of that by watching the starlight as it passes through the planet’s atmosphere.

“This new planet we’ve discovered is still weird – but it’s one step closer to being somewhat like our neighborhood planets.”

Jennifer Burt, Paper Lead Author, NASA-JPL.

Since TOI-1231 b spends so much time in front of its star relative to other TESS planets, missions like the JWST will get a much better look at it.

But it’s not only the planet’s orbital period that makes it an ideal target. Its size relative to its star also helps. Since the star is so small, the planet blocks out more of its light than if the planet and star were more similar to Earth and the Sun. “In a sense, this creates a larger shadow on the surface of the star, making planets around M dwarfs more easily detectable and easier to study,” the press release says.

The paper outlining TOI 1321-b’s discovery is titled “TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf NLTT 24399.” The lead author is NASA JPL scientist Jennifer Burt. The paper will be published in The Astrophysical Journal but is up now on the pre-press site arxiv.org.

“Working with a group of excellent astronomers spread across the globe, we were able to assemble the data necessary to characterize the host star and measure both the radius and mass of the planet,” said Burt in a press release. “Those values in turn allowed us to calculate the planet’s bulk density and hypothesize about what the planet is made out of. TOI-1231 b is pretty similar in size and density to Neptune, so we think it has a similarly large, gaseous atmosphere.”

The team that found TOI-1321 b says the planet is similar to Neptune and likely has a similar gaseous atmosphere. Image Credit: NASA/JPL

The new planet has a radius of about 3.65 times that of Earth. It has an orbital period of 24.26 days and mass of about 15.5 Earth masses. The star it orbits is an M-dwarf star about 90 light years away in the constellation Vela.

The planet is a lot closer to its star than the Earth is to the Sun. But 1321 b is about the same temperature because its star is so much cooler than the Sun. That lower temperature also makes it a desirable object for further study with the JWST and other telescopes. Its equilibrium temperature is only about 330 Kelvin, making it one of the coolest small planets available for atmospheric study. For comparison, Earth’s mean temperature is about 288 Kelvin, and an ultra-Hot Jupiter can have a dayside temperature of up to 2700 K, hotter than many stars.

“TOI-1231 b is one of the only other planets we know of in a similar size and temperature range, so future observations of this new planet will let us determine just how common (or rare) it is for water clouds to form around these temperate worlds,” said Burt.

This image from the study shows the transmission spectroscopy metric (TSM) values for some small exoplanets with temperature less than 1000 Kelvin. The four filled-in planets with black circles and labels have undergone follow-up study with the Hubble. TOI-1231 b is next, and gives scientists another opportunity to study the atmospher of small, cooler planets. The horizontal axis shows the J magnitude of the stars the planets orbit. Image Credit: Burt et al 2021.

Adding to its desirability as a target, it has a high systemic radial velocity. Astronomers are especially excited about that because it may permit the observation of low-velocity hydrogen atoms escaping from the atmosphere. TOI-1231 b’s characteristics and relationship with its star are similar to another star named GJ-436 and its planet GJ-436 b. GJ-436 b is well-known for its atmospheric escape, so astronomers think that the newly-discovered exoplanet will also experience atmospheric escape, though at a much lower rate than GJ-436 b. Hydrogen is the most likely escape culprit, but it’s hard to see because of the presence of interstellar gas. But TOI-1232 b is travelling away from Earth very quickly, making the hydrogen more visible.

Diana Dragomir is one of the co-authors of the paper. In the same press release she said, “The low density of TOI-1231 b indicates that it is surrounded by a substantial atmosphere rather than being a rocky planet. But the composition and extent of this atmosphere are unknown!” said Dragomir. “TOI-1231 b could have a large hydrogen or hydrogen-helium atmosphere, or a denser water vapor atmosphere. Each of these would point to a different origin, allowing astronomers to understand whether and how planets form differently around M dwarfs when compared to the planets around our Sun, for example. Our upcoming HST observations will begin to answer these questions, and JWST promises an even more thorough look into the planet’s atmosphere.”

It’ll be a while before the JWST can train its sensors on the newly-discovered exoplanet, even though the space telescope is launching soon (™). But the Hubble is ready to go. In fact, one of the paper’s numerous authors is planning to observe TOI-1231 b later this month.

The James Webb Space Telescope in June 2020. We’ve been told it’ll launch soon. Image Credit: NASA/JPL

All of these exoplanet discoveries are showing us the wide variety present in other solar systems. There are some downright weird planets out there, at least compared to Earth. But this one is more similar to Earth than all the Hot Jupiters we’ve found, and while it’s still different, it at least might teach us something about our own Solar System and the planets that reside there.

One of the most intriguing results of the last two decades of exoplanet science is that, thus far, none of the new planetary systems we’ve discovered look anything like our own solar system,” said Burt. “They’re full of planets between the size of Earth and Neptune on orbits much shorter than Mercury’s, so we don’t have any local examples to compare them to. This new planet we’ve discovered is still weird – but it’s one step closer to being somewhat like our neighborhood planets. Compared to most transiting planets detected thus far, which often have scorching temperatures in the many hundreds or thousands of degrees, TOI-1231 b is positively frigid.”

## Investigating Baked Meteorites Yields Clues to Planetary Atmospheres

The early atmospheres of rocky planets are thought to form mostly from gases released from the surface of the planet as a result of the intense heating during the accretion of planetary building blocks and later volcanic activity early in the planet’s development. Credit: Illustration by Dan Durda/Southwest Research Institute

The gases released from meteorite samples heated in a high-temperature furnace can tell scientists about the initial composition of the atmospheres of rocky exoplanets.

In a novel laboratory investigation of the initial atmospheres of Earth-like rocky planets, researchers at UC Santa Cruz heated pristine meteorite samples in a high-temperature furnace and analyzed the gases released.

Their results, published April 15 in Nature Astronomy, suggest that the initial atmospheres of terrestrial planets may differ significantly from many of the common assumptions used in theoretical models of planetary atmospheres.

“This information will be important when we start being able to observe exoplanet atmospheres with new telescopes and advanced instrumentation,” said first author Maggie Thompson, a graduate student in astronomy and astrophysics at UC Santa Cruz.

The early atmospheres of rocky planets are thought to form mostly from gases released from the surface of the planet as a result of the intense heating during the accretion of planetary building blocks and later volcanic activity early in the planet’s development.

“When the building blocks of a planet are coming together, the material is heated and gases are produced, and if the planet is large enough the gases will be retained as an atmosphere,” explained coauthor Myriam Telus, assistant professor of Earth and planetary sciences at UC Santa Cruz. “We’re trying to simulate in the laboratory this very early process when a planet’s atmosphere is forming so we can put some experimental constraints on that story.”

The researchers analyzed three meteorites of a type known as CM-type carbonaceous chondrites, which have a composition considered representative of the material from which the sun and planets formed.

Samples from three carbonaceous chondrite meteorites — Murchison, Jbilet Winselwan, and Aguas Zarcas — were analyzed in the outgassing experiments. Credit: Image courtesy of M. Thompson

“These meteorites are left over materials from the building blocks that went into forming the planets in our solar system,” Thompson said. “Chondrites are different from other types of meteorites in that they didn’t get hot enough to melt, so they have held onto some of the more primitive components that can tell us about the composition of the solar system around the time of planet formation.”

Working with materials scientists in the physics department, the researchers set up a furnace connected to a mass spectrometer and a vacuum system. As the meteorite samples were heated to 1200 degrees Celsius, the system analyzed the volatile gases produced from the minerals in the sample. Water vapor was the dominant gas, with significant amounts of carbon monoxide and carbon dioxide, and smaller amounts of hydrogen and hydrogen sulfide gases also released.

According to Telus, models of planetary atmospheres often assume solar abundances — that is, a composition similar to the sun and therefore dominated by hydrogen and helium.

“Based on outgassing from meteorites, however, you would expect water vapor to be the dominant gas, followed by carbon monoxide and carbon dioxide,” she said. “Using solar abundances is fine for large, Jupiter-size planets that acquire their atmospheres from the solar nebula, but smaller planets are thought to get their atmospheres more from outgassing.”

The researchers compared their results with the predictions from chemical equilibrium models based on the composition of the meteorites. “Qualitatively, we get pretty similar results to what the chemical equilibrium models predict should be outgassed, but there are also some differences,” Thompson said. “You need experiments to see what actually happens in practice. We want to do this for a wide variety of meteorites to provide better constraints for the theoretical models of exoplanetary atmospheres.”

Other researchers have done heating experiments with meteorites, but those studies were for other purposes and used different methods. “A lot of people are interested in what happens when meteorites enter Earth’s atmosphere, so those kinds of studies were not done with this framework in mind to understand outgassing,” Thompson said.

The three meteorites analyzed for this study were the Murchison chondrite, which fell in Australia in 1969 Jbilet Winselwan, collected in Western Sahara in 2013 and Aguas Zarcas, which fell in Costa Rica in 2019.

“It may seem arbitrary to use meteorites from our solar system to understand exoplanets around other stars, but studies of other stars are finding that this type of material is actually pretty common around other stars,” Telus noted.

Reference: “Composition of terrestrial exoplanet atmospheres from meteorite outgassing experiments” by Maggie A. Thompson, Myriam Telus, Laura Schaefer, Jonathan J. Fortney, Toyanath Joshi and David Lederman, 15 April 2021, Nature Astronomy.
DOI: 10.1038/s41550-021-01338-8

In addition to Thompson and Telus, the coauthors of the paper include Jonathan Fortney, Toyanath Joshi, and David Lederman at UC Santa Cruz and Laura Schaefer at Stanford University. This research was supported by NASA and the ARCS Foundation.

## Astronomers Map a Distant Super-Earth, but It’s a Molten Hell

Forty light-years from Earth lies the binary star 55 Cancri, a cool red dwarf (55 Cancri B) orbiting a star not too different than the Sun (55 Cancri A), though about twice as old. And orbiting closer in to this Sun-like star are at least five planets. One of them, called 55 Cancri e, is basically hell.

It has a radius less than twice Earth’s, and just over eight times our mass. That makes it a super-Earth, bigger than us but smaller than a gas or ice giant like Neptune. It’s a bit denser than Earth, and the surface gravity is more than twice Earth’s too.

It orbits the star on a very tight path, just a couple of million kilometers over the star’s surface. It screams around the star so quickly its year is a mere 18 hours long.

Jason Rowe/NASA Ames/SETI Institute/Prof. Jaymie Matthews, UBC

And it’s hot. Really hot. How hot? Well, that depends on what you mean. For the first time, astronomers were able to map the temperature changes across the planet, and what they found is that 55 Cancri e is a place you really, really don’t want to be. It’s 1,100° C (2,000° F) there … on the night side.

On the day side, it’s a crispy 2,400° C, or 4,400° F. You might want to bring your SPF a billion. *

But wait! It gets weirder! Bear with me this’ll take a moment to explain.

The planet orbits the star so closely that from Earth, we see it pass physically in front of the star once per orbit (called a transit) where it blocks a fraction of the star’s light, and then passes behind the star half an orbit later so the star blocks the planet. Over the course of an orbit the planet undergoes a complete set of phases as seen from Earth, like the phases of the Moon. When it’s in front of the star it’s “new,” and we see its unlit backside. As it circles around it’s a crescent, then half full, then gibbous, then full … but when it’s exactly full, it’s behind the star. Then it pops out again, and we see the phases in reverse.

We don’t see the phases, actually. The planet is too far away from us and too close to the star. But as it undergoes these phases, the amount of light we see from the planet changes. Incredibly, using Spitzer Space Telescope (and some pretty fancy data processing techniques), a team of astronomers was able to measure this teeny change in the light from the planet.

Demory et al., from the paper (annotated by Phil Plait)

This is called an orbital phase diagram. Along the horizontal axis is time in units of one orbit. In that case, 0 is when the planet is directly between us and the star, 0.25 is a quarter of the way around, 0.5 is when it’s directly behind the star, and 1 is when it’s back in front of the star again.

The y axis is brightness, such that 0 is when we only see the star (the planet is hidden). So at x=0, the total light is lower because the planet blocks starlight at x=0.5 we see just the star, and in between we see the planet plus the star.

Right away, you can see that graceful long up-and-down curve of light across the whole plot. That’s the light of the planet changing with its phase! If we were just seeing the star, that would be a flat horizontal line. But as the planet circles around to the back side of the star its phase increases, and we see more light from it. The reverse is true as it comes back around.

Right away, that’s pretty boggling. We’re seeing the change in light from a planet 400 trillion kilometers away! Wow!

But this is where the weird part comes in. The planet is so close to the star that the gravity (really, the tides) from the star should lock the planet’s day to its year, so that it spins once every 18 hours as it goes around the star once every 18 hours.

The brightest spot on the planet should be directly under the star, what’s called the substellar point. That faces us right before the planet goes behind the star, so the whole system should be brightest when the planet is just about to be blocked.

But look closer. The brightness does peak before the eclipse, but then it dips a little. That means the brightest spot on the planet is not the substellar point. For some reason, the hottest part of 55 Cancri e is about 40° east of that point.

## Astronomers discover nearby exoplanet with substantial atmosphere

June 8 (UPI) -- Astronomers have discovered a temperate, sub-Neptune-sized exoplanet orbiting a nearby M dwarf star.

Initial observations of the Earth-like planet, described Wednesday in the Astronomical Journal, suggest the alien world boasts a substantial atmosphere -- which is sure to inspire followup studies for years to come.

The exoplanet, TOI-1231 b, was initially spotted using photometric data from the Transiting Exoplanet Survey Satellite, or TESS.

Followup observations captured using the Planet Finder Spectrograph on the Magellan Clay telescope at Las Campanas Observatory in Chile allowed scientists to work out the planet's radius, mass and density.

TESS trains its gaze on sections of the night sky for nearly a month at time, capturing images of thousands of stars.

Astronomers, citizen scientists and algorithms scan the data for dimming patterns made by exoplanets as they orbit across the face of their host stars.

Because M dwarf stars are smaller and dimmer than stars like the sun, the transits of nearby stars have a more pronounced dimming effect.

Still, astronomers were lucky that TESS picked up on the presence of TOI-1231 b, which takes 24 days to complete an orbit around its host star.

To confirm the presence of an exoplanet, TESS typically needs to capture two transits, or the completion of an orbit.

Because TESS only stares at one section fo the sky for 28 days, the average orbital period of exoplanets spotted by TESS is 14 days.

Scientists said TESS caught TOI-1231 b at just the right time.

"Working with a group of excellent astronomers spread across the globe, we were able to assemble the data necessary to characterize the host star and measure both the radius and mass of the planet," lead study author Jennifer Burt said in a press release.

"Those values in turn allowed us to calculate the planet's bulk density and hypothesize about what the planet is made out of. TOI-1231 b is pretty similar in size and density to Neptune, so we think it has a similarly large, gaseous atmosphere," said Burt, a scientist at NASA's Jet Propulsion Laboratory.

In addition to enabling a more robust exoplanet transiting signal, an M dwarf star's small stature also makes it easier for astronomer to calculate the masses of newly discovered exoplanets, as the ratio of planet to stellar mass is larger.

Astronomers calculate an exoplanet's mass by measuring the planet's slight gravitational effect on its host star -- the smaller the star, the larger an exoplanet's gravitational effect will be.

"Even though TOI-1231 b is eight times closer to its star than the Earth is to the sun, its temperature is similar to that of Earth, thanks to its cooler and less bright host star," study co-author Diana Dragomir said in the release.

"However, the planet itself is actually larger than earth and a little bit smaller than Neptune -- we could call it a sub-Neptune," said Dragomir, an assistant professor of astronomy at the University of New Mexico.

What has astronomers most excited about TOI-1231 b is its atmosphere.

Previous studies suggests small, cool planets similar to the newly discovered exoplanet are capable of holding water in the upper layers of their atmosphere.

"The low density of TOI-1231 b indicates that it is surrounded by a substantial atmosphere rather than being a rocky planet. But the composition and extent of this atmosphere are unknown!" said Dragomir.

"TOI-1231 b could have a large hydrogen or hydrogen-helium atmosphere, or a denser water vapor atmosphere. Each of these would point to a different origin, allowing astronomers to understand whether and how planets form differently around M dwarfs when compared to the planets around our sun, for example," Dragomir said.

The researchers said they hope future observations will help them work the exoplanet's atmospheric composition, as well as determine how rare or common such exoplanets are.

## What is the temperature on the moon?

What is the temperature on the Earth’s Moon? Unlike temperatures on our planet, the temperatures on the moon are extreme and severe. The exact temperature on the moon depends on the location of the Sun.

Due to the moon’s tilt on its axis and the way it rotates around the Earth, the moon is always lit up by the sun on one side and dark on the other. One “day” on the moon equals about 27 Earth days. Half of the moon will be in daytime for about fourteen Earth days, while the side in the darkness will experience nighttime for also fourteen Earth days.

When illuminated by the sun, the surface of the moon can reach up to 127 degrees Celsius (260 Fahrenheit). When the illuminated side moves into darkness, the temperature falls significantly. Since the sun no longer heats the surface, the moon’s surface can drop to -232 Celsius (-387 F). These are the coldest temperatures in our solar system, which means the surface of the moon becomes colder than that of Pluto.

The poles of the moon and the craters are the places that reach the most extreme temperatures. Due to its minimal tilt, the moon does not experience seasons. There are regions and places on the moon, specifically at the poles, where the sun cannot reach, making these spots the coldest places on the moon. There are a few craters located at the poles of the moon that have not been touched by sunlight for billions of years. NASA scientists have found signs of ice in these shadowy places and cratered regions. Scientists also discovered that some of these craters and shadowed areas could reach -272 degrees Celsius (-458 degrees Fahrenheit).

One reason for such extreme temperatures on the moon is the atmosphere. Unlike our planet, the moon does not have an atmosphere. On Earth, sunlight hits the ground and releases radiation. The radiation then moves upward, but it because trapped by our atmosphere and heats our planet. The atmosphere also diffuses radiation, keeping the Earth from becoming extremely hot. The moon has no atmosphere to trap heat or limit the power of the sun, leaving it to become extremely hot and cold.

The Earth’s core is another element that helps warm our planet. The core heats the innermost layers of our planet, which, in turn, warms the upper layers (where we stand). However, unlike our planet, the moon’s core is not warm enough to warm the upper layers. While the moon is smaller than the Earth, the core temperature of the moon does not get hot enough to warm the other layers that compose it.

The temperature of the moon ranges from extremely hot (127 Celsius) to extremely cold (-272 Celsius). Its temperature depends on whether you measure the temperature in the sun or the temperature in the dark. The temperature also depends on whether or not you measure a deep crater or a hill. Nonetheless, the temperatures on the moon are extreme, causing us to carefully consider how we build our lunar instruments and suits for our astronauts.

## Clouds, haze and baby snowflakes

As mentioned earlier, Pluto may also have clouds and haze, made of the very constituents of its atmosphere: molecular nitrogen, and some carbon monoxide and methane. The presence of clouds, however, is dependent on the existence of a temperature gradient, like that on Earth.

"On Earth, there is what we call a troposphere, where the temperature decreases with altitude, causing water to supersaturate and form clouds," Summers said. "Above the Earth's troposphere, the temperature increases again in the stratosphere. On Pluto, there is probably not a very thick troposphere. In fact, it may be only 1 km to 2 km (0.6 to 1.2 miles) thick, so any clouds would have to be very close to the surface."

And with clouds must come some form of rain or, at Pluto's distance from the sun, snow. But this snow is not the kind we see here on Earth — and not just because of its composition, but also because of how tenuous Pluto's atmosphere is.

"[O]n Earth, we have a very thick atmosphere with lots of condensable water vapor," Summers said. "But on Pluto, with its thin atmosphere, I think any condensed particles would be very small, perhaps microns in size, so they would probably not form as snowflakes. But they could still be regular, with hexagonal symmetry — like 'baby' snowflakes on Earth."

## In the air

The first study, which appears in Nature Astronomy, looks at the atmospheres of several of the planets, but not directly. Instead, it relies on the Hubble to observe the star's light as a planet passes in front of it. A tiny fraction of the photons will have passed through the planet's atmosphere on their way to Earth. Any colors of light that are absorbed or scattered by the gases in the atmosphere will be missing from that fraction, making it possible to infer the atmosphere's composition.

It's possible, but not easy. In this case, the planets were observed as the Hubble Space Telescope orbited through something called the South Atlantic Anomaly, where the Earth's radiation belts dip to meet its orbit. Images taken during this time have more radiation-induced noise and lower resolution, as the telescope shuts down its fine-pointing hardware.

While the results don't tell us what's in the atmosphere, they do tell us what's not likely to be there: lots of hydrogen. The spectrum of the atmospheres of these planets is relatively featureless, whereas hydrogen would absorb at a number of different wavelengths covered by the Hubble data. It's possible to get something that looks like this if a lot of clouds are present, but there's no obvious way of generating the aerosols needed for clouds in a hydrogen rich atmosphere. Earlier work had reached this conclusion for the innermost planets the new data excludes hydrogen for planets d, e, and f. That only leaves TRAPPIST-1 g for further study.

That doesn't tell us what's in these atmospheres. For many of the planets, a variety of compositions are consistent with the data. For b and c, for example, the authors say the options include "atmospheres dominated by water, nitrogen, or carbon dioxide tenuous atmospheres composed of a variety of chemical species and atmospheres dominated by aerosols." But ruling out hydrogen is significant for two reasons. One, it's likely that most planets start out with hydrogen-rich atmospheres, so this suggests these planets have evolved a bit. The second is that hydrogen is a potent greenhouse gas and, so, would have a strong influence on the planet's temperature.

## TEST BANK 21ST CENTURY ASTRONOMY THE SOLAR SYSTEM 5TH EDITION BY KAY

Short Answer: Describe the origin of terrestrial planets’ secondary atmospheres.

Short Answer: Establish why some terrestrial planets do not have secondary atmospheres today.

Multiple Choice: 4, 5, 6, 7, 8, 11

9.2 Secondary Atmospheres Evolve

Illustrate why planetary mass affects a planet’s ability to retain its atmosphere.

Describe the atmospheric greenhouse effect.

Multiple Choice: 17, 18, 21, 22, 23, 24

Short Answer: Illustrate how greenhouse gases cause the greenhouse effect.

Multiple Choice: 14, 19, 20, 25, 26, 29

Compare and contrast the causes for the terrestrial planets to have their current atmospheres.

Multiple Choice: 13, 15, 16, 27, 28

9.3 Earth’s Atmosphere Has Detailed Structure

Explain how Earth developed an oxygen-rich atmosphere.

Multiple Choice: 30, 31, 32, 33, 34, 35, 36, 37, 38, 40, 41, 58

Differentiate the temperature, density, and composition of the different layers of our atmosphere.

Multiple Choice: 42, 43, 45, 46, 47, 48, 50, 51, 55

Short Answer: 10, 11, 12, 13, 15, 16, 17, 18, 19

Illustrate how our magnetosphere causes auroras.

Relate a planet’s rate of rotation to its wind patterns.

Multiple Choice: 44, 49, 53, 54, 56

9.4 The Atmospheres of Venus and Mars Differ from Earth’s

Describe the atmospheric characteristics of Venus and Mars.

Multiple Choice: 59, 62, 63, 67, 69, 70

Characterize the causes for the atmospheric characteristics of Venus and Mars.

Multiple Choice: 57, 60, 61, 64, 65

9.5 Greenhouse Gases Affect Global Climates

Compare and contrast weather and climate.

Explain the different factors that cause climate change on a planet.

Summarize the evidence that human activity is causing global climate change.

Assess whether a planet will hold onto its atmosphere based on its escape speed at atmospheric temperature.

Compute the average molecular speed of atmospheric gas.

1. The major chemical component of the air we breathe today was deposited on Earth primarily via
1. volcanic eruptions.
2. cometary impacts.
3. asteroid impacts.
4. chemical reactions in Earth’s oceans.
1. Its mass is small.
2. It has a high temperature.
3. It is close to the Sun.
4. Its escape velocity is low.
5. all of the above
1. They were too hot and their escape velocities too low to hold onto them.
2. The solar wind was too strong and blew these gases off the planets.
3. Their high surface temperatures made the gas chemically react with the rock.
4. The initial gases were so heavy when the planet differentiated that they sank to the core.
1. The average velocity of nitrogen atoms is 0.4 km/s, and nitrogen does not escape.
2. The average velocity of nitrogen atoms is 1.0 km/s, and nitrogen does not escape.
3. The average velocity of nitrogen atoms is 1.0 km/s, and nitrogen escapes.
4. The average velocity of nitrogen atoms is 4.5 km/s, and nitrogen does not escape.
5. The average velocity of nitrogen atoms is 4.5 km/s, and nitrogen escapes.
1. No, the average velocity of water molecules is 0.9 km/s.
2. Yes, the average velocity of water molecules is 0.9 km/s.
3. Yes, the average velocity of water molecules is 2.1 km/s.
4. No, the average velocity of water molecules is 2.1 km/s.
5. Yes, the average velocity of water molecules is 19 km/s.
1. No, the average velocity of hydrogen atoms would be 0.8 km/s.
2. No, the average velocity of hydrogen atoms would be 3.9 km/s.
3. Yes, the average velocity of hydrogen atoms would be 3.9 km/s.
4. Yes, the average velocity of hydrogen atoms would be 25 km/s.
5. No, the average velocity of hydrogen atoms would be 25 km/s.
1. If an average hydrogen atom in Earth’s atmosphere has a velocity of 2.5 km/s, what would be the average velocity of an oxygen molecule in Earth’s atmosphere? Note that the atomic mass of an oxygen atom is 16 times that of a hydrogen atom.
1. 16 km/s
2. 5 km/s
3. 62 km/s
4. 44 km/s
5. 25 km/s
1. Water vapor would escape because 1/6 times the escape velocity is 0.51 km/s.
2. Water vapor would not escape because 1/6 times the escape velocity is 1.7 km/s.
3. Water vapor would escape because 1/6 times the escape velocity is 0.42 km/s.
4. Water vapor would not escape because 1/6 times the escape velocity is 2.6 km/s.
5. Water vapor would escape because 1/6 times the escape velocity is 1.3 km/s.
1. volcanism
2. accretion
3. oxidation
4. comet impacts
5. All of the above contributed gases to Earth’s secondary atmosphere.
1. ammonia delivered by comet impacts.
2. photosynthesis done by algae and plants.
3. oxidation of silicate-rich minerals.
4. rock delivered by asteroid impacts.
5. its primary atmosphere.
1. Mercury
2. Venus
3. Mars
4. the Moon
5. Earth
1. Water, H2O (atomic mass = 18)
2. Carbon dioxide, CO2 (atomic mass = 44)
3. Nitrogen (atomic mass = 28)
4. Oxygen (atomic mass = 32)
5. Hydrogen, H2 (atomic mass = 2)
1. 10 10
2. 200 100
3. 2,000 2
4. 2 10
5. 1,000 200
1. It would rapidly escape into space.
2. It would dissociate into carbon and oxygen.
3. It would collect as ice on the north and south poles.
4. It would cause a runaway greenhouse effect.
1. high surface temperatures
2. volcanic activity
3. cometary impacts
4. a lack of asteroid impacts
5. the greenhouse effect
1. Venus, Earth, Mars, Mercury
2. Venus, Mars, Earth, Mercury
3. Mercury, Mars, Earth, Venus
4. Mars, Venus, Mercury, Earth
1. oxygen and nitrogen.
2. methane and ozone.
3. carbon dioxide and water vapor.
4. hydrogen and helium.
5. methane and ammonia.
1. infrared
2. visible
3. ultraviolet (UV)
5. microwave
1. They would evaporate.
2. They would freeze over.
3. They would be rapidly absorbed into the surface rocks.
4. They would dissociate into ozone and hydrogen.
1. It easily absorbs UV radiation.
2. It easily absorbs visible light.
3. It easily absorbs infrared radiation.
4. It easily reacts chemically with rock.
5. It easily photodissociates in the upper atmosphere.
1. 0 K.
2. 35 K.
3. 5 K.
4. 35 K.
5. 350 K.
1. trapping of infrared radiation by the atmosphere.
2. accentuated growth of plants near the equator, compared to other regions.
3. capturing of visible and UV radiation from the Sun the atmosphere.
4. shielding of life-forms from solar UV radiation by the ozone layer.
1. If it were not for the greenhouse effect on Earth,
1. there would be no liquid water on Earth.
2. life as we know it would not have developed on Earth.
3. it would be a much colder planet.
4. there would be no oxygen in Earth’s atmosphere.
5. All of the above are results of the greenhouse effect.
1. The water vapor would relieve the greenhouse effect and decrease Venus’s surface temperature.
2. Water droplets would condense into rain and form lakes on Venus’s surface.
3. The water vapor would chemically react with carbon dioxide and form acid rain.
4. UV light would break apart the water molecules, and the hydrogen would be lost into space.
5. It would rise into the atmosphere and form hurricane-like storms.
1. Venus has slow, retrograde rotation, and its seasons are very long.
2. Venus has many active volcanoes that release heat into its atmosphere.
3. Venus has a very thin atmosphere, and more sunlight falls onto its surface.
4. Venus has a strong greenhouse effect.
5. Venus has a highly eccentric orbit and is sometimes much closer to the Sun than other times.
1. escape into outer space.
2. remain in liquid form.
3. vaporize and form clouds in the atmosphere.
4. be absorbed into rocks.
1. Venus is covered with clouds.
2. Earth has a large amount of liquid water.
3. Some form of ice does exist on Mars, but it does not have large amounts of liquid water.
4. The planets in order from the least to most dense atmospheres are Venus, Earth, and Mars.
5. all of the above
1. It has escaped into outer space.
2. It is bound up in the plant life on Earth.
3. It is bound up in rocks.
4. It is dissolved into the oceans.
5. It is still in the atmosphere in the form of complex molecules.
1. The majority of Earth’s carbon dioxide escaped into space because of its hotter temperature, whereas Venus’s carbon dioxide remains gravitationally bound to Venus.
2. The majority of Earth’s carbon is now bound up in rock, whereas Venus’s remains in its atmosphere.
3. Earth lost more of its secondary atmosphere because it was bombarded by more planetesimals than Venus.
4. The majority of Earth’s carbon was absorbed by plants during photosynthesis.
5. Earth and Venus still have equal amounts of carbon dioxide in their atmospheres.
1. life on Earth.
2. Earth’s plate tectonics.
3. differences in the greenhouse effect.
4. the presence of liquid water.
5. differing distances from the Sun.
1. 3 billion years ago
2. 1 billion years ago
3. 5 billion years ago
4. 25 billion years ago
5. 1 billion years ago
1. It has significantly declined.
2. It has significantly increased.
3. It kept increasing up to 2 billion years ago but has been declining ever since.
4. It hasn’t changed.
1. search for absorption from nitrogen in their atmospheres.
2. search for absorption from oxygen in their atmospheres.
3. search for emission lines from water vapor in their atmospheres.
4. search for carbon dioxide on their moons.
1. Carbon dioxide
2. Water vapor
3. Nitrogen
4. Oxygen
5. Helium
1. the atmosphere would become less dense.
2. oxygen would disappear from the atmosphere.
3. the atmosphere would become hotter.
4. nitrogen would disappear from the atmosphere.
5. the amount of water vapor in the atmosphere would decrease.
1. 100 million trees and plants
2. 1 billion trees and plants
3. 250 million bacteria and algae
4. 5 billion bacteria and algae
5. 2,000 animals and humans
1. 4 billion years
2. 1 billion years
3. 400 million years
4. 1 million years
5. Oxygen was always a primary component of Earth’s atmosphere.
1. For the first 1 billion years of Earth’s evolution, the fraction of oxygen in its atmosphere was approximately
1. half of what it is today.
2. 2 times what it is today.
3. 10 times what it is today.
4. the same as it is today.
1. Those are the locations where the atmosphere is thinner, letting particles penetrate.
2. The poles are pointing toward the Sun, so they receive more solar wind particles.
3. The oxygen atoms responsible for auroral emission only exist near the poles.
4. Charged particles are forced to flow along Earth’s magnetic field lines, which come out of Earth’s poles.
1. 3 billion years ago
2. 1 billion years ago
3. 6 billion years ago
4. 25 billion years ago
5. 1 billion years ago
1. oxygen
2. methane
3. water vapor
4. oxygen, methane, or water vapor
1. UV
2. X-ray
3. gamma ray
4. infrared
5. microwave
1. how the temperature varies with altitude.
2. how the pressure varies with altitude.
3. how the density varies with altitude.
4. different temperature ranges.
5. different pressure ranges.
1. on Mars
2. on Mercury
3. on Venus
4. nowhere else in the solar system
1. one
2. two
3. three
4. four
5. five
1. All weather and wind on Earth are a result of convection in the
2. According to the following figure, as you increase in altitude in Earth’s lower atmosphere, the atmospheric pressure ________ dramatically at a(n) _________ rate.
1. increases increasing
2. increases decreasing
3. decreases decreasing
4. decreases increasing
5. decreases constant
1. the troposphere and the thermosphere.
2. the mesosphere and the stratosphere.
3. the thermosphere and the stratosphere.
4. the troposphere and the mesosphere.
5. the troposphere and the stratosphere.
1. strong updrafts from the equator and air sinking near the poles.
2. uneven heating of the surface and rotation of the planet.
3. water condensation onto mountains.
4. hot air rising and cool air sinking.
1. higher-energy particles in the solar wind
2. convection
3. the ozone layer absorbing UV light
4. charged particles trapped by magnetic fields
5. the greenhouse effect
1. the Moon’s tidal force.
2. the solar wind.
3. Earth’s own gravity.
4. asymmetries in the shape of Earth’s core.
5. Earth’s elliptical orbit.
1. gases fluorescing in the atmosphere because of collisions with solar wind particles.
2. the magnetosphere of Earth touching its atmosphere.
3. the ozone layer being destroyed by UV light.
4. a product of the atmospheric greenhouse effect.
5. scattering of sunlight from particles in Earth’s stratosphere.
1. rotate in the same direction
2. rotate in the opposite direction
3. move from east to west
4. have larger wind speeds
5. cause more damage
1. What is the main reason Hadley circulation in a planet’s atmosphere breaks up into zonal winds?
1. convection driven by solar heating
2. heating from the solar wind
3. hurricanes developing along the planet’s equator
4. a planet’s rapid rotation
5. heating from the greenhouse effect
1. destruction of ozone.
2. acid rain.
3. violent storms.
2. the Coriolis effect.
3. the heat of vaporization of water.
4. electrical conductivity of water.
5. the greenhouse effect.
1. There should be almost no change in temperature.
2. by tens of K (like Earth)
3. by hundreds of K (like Mercury)
4. The answer depends on where Venus is in its orbit around the Sun.
1. blue light from the sun is more readily scattered by molecules in the atmosphere than red light.
2. of reflected light from the oceans.
3. red light from the sun is more readily scattered by molecules in the atmosphere than blue light.
4. molecules that make up Earth’s atmosphere radiate preferentially at blue wavelengths.
5. the Sun radiates more blue light than other wavelengths.
1. We cannot see down to its surface in visible light.
2. Its surface is very smooth.
3. Venus looks highly reflective.
4. The surface pressure is 100 times higher than on Earth’s surface.
1. winds moving from its equator to its poles.
2. heated air escaping from its volcanoes moving along the equator.
3. winds moving from its poles to its equator.
4. heated air escaping from active tectonic plates.
1. carbon dioxide.
1. Water melts and forms large pools of liquid.
2. The polar ice caps disappear.
3. Large planet-wide dust storms.
4. The entire planet changes color.
1. they are made of a very thin layer of carbon dioxide.
2. they are made of a thick layer of water vapor.
3. they extend much farther from the rocky surface.
4. they are made of a thin layer of light atoms such as helium, sodium, and argon.
1. it is very slow.
2. it is very slow and retrograde.
3. its obliquity is 90 degrees.
4. it is very fast.
5. it is very fast and retrograde.
1. Venus’s surface temperature is fairly uniform from the equator to the poles because
1. Venus rotates very rapidly, which causes strong zonal winds.
2. Venus is covered by a thick cloud layer that absorbs most of the sunlight that falls on it.
3. the carbon dioxide in Venus’s atmosphere efficiently emits infrared radiation.
4. Venus rotates slowly so Coriolis forces do not disrupt Hadley circulation.
5. Venus’s orbit is nearly perfectly circular.
1. the production of carbon dioxide.
2. the production of acid rain.
3. the destruction of ozone over decades and centuries.
4. the destruction of water in the upper atmosphere.
1. there is not enough oxygen in the atmosphere.
2. the range in temperature between day and night is too large.
3. the flux of UV radiation reaching the surface is too high.
4. the atmospheric pressure would be too low.
5. all of the above
1. global warming.
2. the growth of the ozone hole.
3. the burning of fossil fuels.
4. increased energy output from the Sun.
5. increased magnetic activity in the Sun.
1. melts and forms liquid pools on the surface.
2. boils off the surface and escapes into outer space.
3. sublimates and goes directly into the gaseous phase.
4. remains frozen because the temperature remains below the freezing point.
5. melts and creates flowing rivers that erode the landscape.
1. they are very small in magnitude, less than 1°C.
2. they occur at irregular time intervals.
3. they are driven by volcanic activity.
4. they occur over much longer time scales (thousands of years).
5. they are driven by emissions of methane gas rather than carbon dioxide.
1. The primary atmospheres of the terrestrial planets formed from hydrogen and helium. Why? What happened to this gas?
2. A gas eventually will escape from a planet’s atmosphere if the average velocity of its atoms exceeds 1/6 times the escape velocity of the planet. If the average velocity of water vapor in Venus’s atmosphere is 0.5 km/s, what would be the average velocity of a single hydrogen atom? If Venus’s escape velocity is 11 km/s, will hydrogen atoms eventually escape?
3. Most of Earth’s present-day atmosphere comes from a combination of what three sources?
4. If the average CO2 molecule in Venus’s atmosphere has a velocity of 0.6 km/s, what would be the velocity for a hydrogen atom in Venus’s atmosphere? Note the mass of a CO2 molecule is 44 times that of a hydrogen atom.
5. What is the origin of Earth’s water?
6. List the three planets shown in the following images in order of decreasing surface temperature, and cite evidence that can be seen in the images that supports your choice.
7. What is the greenhouse effect?
8. Where is most of Earth’s supply of carbon dioxide today?
9. Describe how the closer location of Venus to the Sun compared to Earth led to the runaway greenhouse effect observed on Venus today.
10. Earth’s atmosphere is a (seemingly) enormous blanket roughly 250 km thick. What percentage of Earth’s radius, which is 6,400 km, does this represent? How does it compare to the average depth of the oceans, which is 3 km?
11. If there is 1E4 kg of air above every square meter of the surface of Earth, and Earth is modeled as a sphere of radius 6.4 × 106 m, what is the mass of Earth’s atmosphere, and what fraction is it of the total mass of Earth? Show your calculation.
12. Suppose you go out hiking in the snow on a mountaintop on a cold winter day when the temperature outside is 0°C = 273 K and the pressure is 0.75 bar. If you brought along a package of potato chips that was sealed at sea level when the temperature was 24°C = 297 K, what would have happened to the volume of the bag of chips? By how much will the volume have changed?
13. You take a sealed plastic bag of snacks onto an airline flight where the atmospheric pressure is reduced to 0.8 bar, but the cabin is heated so that the temperature is approximately the same as when you sealed the bag. What will happen to the volume of the bag? By how much will it have changed?
14. According to the following figure, about how long ago did oxygen first appear in Earth’s atmosphere? About how long ago did oxygen reach 50 percent of its current abundance in Earth’s atmosphere?
15. Describe the process(es) responsible for producing rain.
16. Over the last century, why has the ozone hole over Earth grown larger? How long might it take to revert to its former state?
17. Give two reasons why the atmosphere of Earth is warmer near the surface than at higher elevations.
18. Why does the temperature decrease as you go higher up in altitude in the troposphere on Earth?
19. In the stratosphere of Earth’s atmosphere, how does the temperature vary with increasing altitude, and what causes this variation?
20. The global winds on Earth are the result of a combination of what three things?
21. If sunlight cannot penetrate Venus’s cloud layer efficiently, why does the temperature of the planet remain so high?
22. Carbon dioxide levels in Earth’s atmosphere have been rising by about 4 percent per decade because of the use of fossil fuels. If this trend continues, what could happen to Earth?
23. On Mars, water could exist in what form(s): solid, liquid, or gas? How does this vary with the seasons on Mars? Why are the seasonal variations on Mars different in its northern and southern hemispheres?
24. Give three reasons why we believe Venus may currently have active volcanoes.
25. Describe how a weak magnetic field on Mars may lead to loss of its atmosphere over time.
26. How does climate differ from weather?
27. The obliquity of Earth’s rotation axis has remained stable at 23 degrees over its history, whereas that of Mars is believed to have varied from 13 to 40 degrees. Why?
28. Although Earth is known to exhibit long-term natural variations in temperature, scientists are nearly unanimous in believing that the recent rise in temperature is due to human industrial activity. Why?
29. What factors drive the long-term periodic variations in Earth’s average temperature (known as the Milankovitch cycle)?
30. Describe the factors influencing the climate on Earth.

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Albedo is a measurement of the amount of light reflected from the surface of a celestial object, such as a planet, satellite, comet or asteroid. The albedo is the ratio of the reflected light to the incident light:

• 0: a black object that absorbs all light and reflects none and
• 1: a white object that reflects all light and absorbs none.

Planets and satellites with clouds tend to have a high albedo, while rocky objects such as asteroids have a low albedo. The albedo of an object changes with wavelength, depending on the efficiency of reflection for different parts of the electromagnetic spectrum. The albedo of the Earth changes slightly with the seasons, due to differences in the amount of cloud cover and the presence of snow in either hemisphere and at the poles.

The table below gives approximate values of albedo for each of the planets, the Moon and Pluto:

Planet Bond Albedo Geometric Albedo
Mercury 0.12 0.14
Venus 0.75 0.84
Earth 0.30 0.37
Moon 0.12 0.11
Mars 0.16 0.15
Jupiter 0.34
Saturn 0.34
Uranus 0.30
Neptune 0.29
Pluto 0.4 0.44-0.61

Bond albedos – total radiation reflected from an object compared to the total incident radiation from the Sun. Geometric albedos – the amount of radiation relative to that from a flat Lambertian surface which is an ideal reflector at all wavelengths.

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