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Does the big (0.012 Earth masses) Moon of Earth clear away NEAs, Earth orbit crossing asteroids, in a significant way? Venus and Mars don't have large moons, do they therefore have larger or smaller population of near asteroids than Earth would have if it were in the same orbit?
The outer planets have large moons, but also lots of captured asteroids, trojans and centaurs. Does a large moon even help gathering such objects, rather than ejecting them? Moonless Mercury and Venus seem to be pretty clean.
I think you answered your own question with your second paragraph.
According to Newton's law of gravity
- the Gravitational force is directly proportional to the product of the masses and inversely proportional to the square of the distance between them.
- So the biggest body in the neighborhood has the most pulling power provided it agrees with the equation.
- As a consequence Jupiter and the outer planets should win out over Earth and keep them from hitting Earth or at least divert the collision course. Especially since the NEA come from their part of the cosmos.
- I suppose the same logic would also work with the comets.
Please see the following link for more: http://earthsky.org/space/is-it-true-that-jupiter-protects-earth
Earth's asteroid impact rate took a sudden jump 290 million years ago
Looking at impact craters on both the Earth and Moon, a team of scientists found that there may have been a sudden increase in big impact events starting around 290 million years ago. At around that time, they think, asteroid impacts became as much as 2.6 times more common.
Mind you — because some folks worry about this sort of thing — this doesn’t affect anything now. It’s not like we’re suddenly seeing more than twice as many impacts since, like, yesterday. We’re talking about an increase that started before the dinosaurs even got their start.
But why? And how did they figure this out?
Rocks ejected by a nearby impact litter the lunar landscape. They erode over millions of years, allowing planetary scientists to measure their age. For scale, this image is 500 meters wide. Credit: NASA/GSFC/Arizona State University
Second things first. We know that there’s a lack of old craters on the Earth, and it’s always been assumed that’s due to erosion. Wind, water, geologic activity: Over long stretches of time our Earth remakes itself, scrubbing the surface of blemishes like impacts * .
But the evidence for this is lacking. That’s what initially motivated the scientists, to try to see if there’s a way to support this idea. So they looked to the Moon. Our satellite is in the same region of space we are, so should get hit at very close to the same rate as Earth does. The idea is to look at big craters on the Moon, figure out a way to get their ages, do the same on Earth, then compare the two and see what you find.
The problem is getting the lunar crater ages, since very few have absolute ages found for them. But they came up with a clever idea. In a big impact, one that leaves a crater 10 kilometers across or wider, rocks from the lunar bedrock get ejected from the explosion and deposited around the crater. Over long periods of time these erode. Not due to air or water, of course, since the Moon doesn’t have those.
Instead, they erode from tiny micrometeorites raining down constantly. These sandblast the rocks, slowly wearing them away (this doesn’t happen on Earth because our atmosphere stops them). Also, the temperature change from day to night on the Moon is hundreds of degrees Celsius. The rocks are constantly expanding and contracting from this, which causes them to crack and erode.
They figured that by looking at the abundance of rocks around a crater compared to the fine powdery eroded rock material (called regolith), they can get a relative age craters with more intact rocks are younger, and ones with more eroded ones are older.
Craters mapped on the Moon to get their ages (left) show that for a given size there are more younger craters than older ones (right) indicating an increase in impact rates 290 million years ago. Credit: Mazrouei et al.
The Lunar Reconnaissance Orbiter is mapping the lunar surface, and has an instrument on board called DIVINER which maps in the infrared. Just after sunset in a spot on the Moon, the rocks will still be hot while the more insulating regolith won’t be. That can be used to get the rock abundance and the relative ages of craters.
They did this for over 100 craters, and also included a handful of craters whose absolute ages were known from other methods. That changed their relative scale to an absolute one, giving them the actual ages of all their craters.
What they found is very interesting indeed. There’s a split in ages of the craters for a given size there are many more younger craters than older ones. That split occurs about 290 million years ago, implying the moon started to get hit 2.6 times as often starting back then.
Mapping how many craters are younger than a given age (vertical axis) versus age (horizontal, starting at present and going into the past shows a break in slope 290 million years ago, implying in increase in impact rate. Credit: Mazrouei et al.
Here’s the thing: They found the same relation on Earth! Looking at big craters in stable regions on Earth (where erosion isn’t as big a problem), they found that there is a sharp increase in impacts around 290 million years ago, by about the same rate as on the Moon.
This strongly implies that erosion is not why we see fewer older craters, but that it represents an actual increase in impacts starting at that time. To be sure, though, they turned to geology.
Kimberlite is a mineral formed in the upper layer of the Earth’s mantle (as much as 450 km below the surface), which can rise rapidly through the crust in explosive volcanic eruptions. It can be found in vertical structures in the crust called pipes. What the scientists found is that in stable regions of the crust, pipes can be found that are very old, showing that erosion didn’t seem to affect them. But in those same regions they found impact craters still showed that rapid increase at 290 million years ago. If erosion were to blame for that, the older pipes should be eroded as well and less common, but that’s not the case.
Illustration of a near-Earth asteroid, created using actual space images of Earth and the asteroid Mathilde. Credit: Earth: ESA/Rosetta asteroid Mathilde: NASA/NEAR
It looks like there really was an increase in asteroid impacts starting at roughly the end of the Paleozoic Era 290 million years ago. I’ll note that some other scientists had some issues with the methods of the first team, but the first team has responded, rebutting those claims.
So what could be the reason behind this uptick in impacts? The simplest explanation is that there must have been some sort of event out in the asteroid belt, probably a major collision, that created a new population of asteroids that moved inward toward the Sun and started hitting us back then. We know this sort of thing can happen many asteroids belong to families, or groups, that have similar orbital characteristics, meaning they were probably all part of a parent asteroid that suffered a big impact, spreading them out.
Likely that’s what happened some 300 million years ago, and not much later they started raining down on Earth.
Big asteroid impacts are rare events, and the only way to understand them is to dig down (sometimes literally) into the past over long periods of time. They tell us a lot about the Earth’s history and of course their danger to us now, but they can also tell us about what was going on in the solar system hundreds of millions of kilometers away, and hundreds of millions of years in the past, too.
And we’d never be able to figure this out if we weren’t mapping the Moon in detail and in different wavelengths of light. This is why we explore: To find ourselves back home and know it for the first time.
Researchers found asteroids had the potential to cause more death and destruction if smashed into the ground or exploded in the sky above a land mass. Known as an &ldquoair burst,&rdquo the asteroid would also bring a grave outcome had it crashed into the sea, causing a tsunami.
&ldquoThe analysis of average casualty numbers per impactor [asteroid] shows that there is a significant difference in expected loss for airburst and surface impacts and that the average impact over land is an order of magnitude more dangerous than one over water,&rdquo the team wrote.
They also added that larger asteroids pose more of a risk than smaller ones.
Fewer Asteroids Lurk Near Earth Than Thought, NASA Telescope Finds
A NASA space telescope that mapped the entire sky has revealed that fewer potentially threatening asteroids are in orbits near Earth, space agency officials announced today (Sept. 29).
The discovery lowers the number of medium-size asteroids near Earth to 19,500 — nearly a 50 percent drop from the 35,000 space rocks initially estimated — and suggests that the threat to Earth by dangerous asteroids may be "somewhat less than previously thought," NASA officials said in a statement. There are still thousands more of these asteroids, which can be up to 3,300 feet wide, that remain to be found.
"Fewer does not mean none and there are still tens of thousands out there to find," study leader Amy Mainzer, principal investigator for NASA's NEOWISE project at the agency's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. [Photos: Asteroids in Deep Space]
Scientists used NASA's Wide-field Infrared Survey Explorer (WISE), an infrared space telescope, to map the asteroid population near Earth and elsewhere in the solar system. By the end of the telescope's extended mission, called NEOWISE, last year, astronomers had found 90 percent of the largest asteroids near our planet, NASA scientists said.
The WISE space telescope mapped the entire sky twice between January 2010 and February 2011 during its mission, which was aimed at mapping near-Earth asteroids, brown dwarfs, galaxies and other deep space objects. For its near-Earth asteroid search, the space observatory scanned for space rocks that orbited within 120 million miles (195 million kilometers) of the sun. The Earth is about 93 million miles (150 million km) from the sun. [Video: Killer Asteroids, We're WISE to You Now]
The telescope's NEOWISE mission discovered more than 100,000 previously unknown asteroids in the asteroid belt between the orbits of Mars and Jupiter. It spotted 585 asteroids in orbits that brought them near Earth.
The WISE asteroid survey, which NASA says is the most accurate ever performed, also lowered the estimated number of giant asteroids — space rocks the size of a mountain — from 1,000 to 981, with about 911 of those already known, researchers said.
"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," said Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass.
NASA launched the $320 million WISE telescope in December 2009. It spent 14 months scanning the heavens in infrared light before NASA shut it down in February 2011.
Getting to know our near-Earth companion
The video above from NASA showcases in detail the path of the new mini-moon's orbit as it bobs up and down like a tiny float in choppy water. As said, it's small, measuring in at only around 120 feet across and no more than 300 feet wide, which is probably why it has taken so long for scientists to spot it. (It was only just spotted in April 2016.) Its distance from Earth varies from between 38 and 100 times the distance of our planet’s primary moon.
The quasi-satellite was given the label of asteroid 2016 HO3, though surely it ought to be in line for a more charismatic title sometime soon. Scientists also assure that the space rock is no threat to our planet or to our main squeeze, the moon.
"The asteroid's loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth's gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon," said Paul Chodas, manager of NASA's Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California. "The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth."
"Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth's companion for centuries to come," he added.
I recall that capture can occur with three bodies involved
And many asteroids look like dumbbells, being multilobed
Those separate lobes could shift around so as to act like dissipative multiple bodies
by Bob King on January 31, 2015
New video of 2004 BL86 and its moon
Newly processed images of asteroid 2004 BL86 made during its brush with Earth Monday night reveal fresh details of its lumpy surface and orbiting moon. We’ve learned from both optical and radar data that Alpha, the main body, spins once every 2.6 hours. Beta (the moon) spins more slowly.
The images were made by bouncing radio waves off the surface of the bodies using NASA’s 230-foot-wide (70-meter) Deep Space Network antenna at Goldstone, Calif. Radar “pinging” reveals information about the shape, velocity, rotation rate and surface features of close-approaching asteroids. But the resulting images can be confusing to interpret. Why? Because they’re not really photos as we know it.
Another set of images of 2004 BL86 and its moon. Credit: NAIC Observatory / Arecibo Observatory
In the images above, the left to right direction or x-axis in the photo plots the toward and away motion or Doppler shift of the asteroid. You’ll recall that light from an object approaching Earth gets bunched up into shorter wavelengths or blue-shifted compared to red-shifted light given off by an object moving away from Earth. A more rapidly rotating object will appear larger than one spinning slowly. The moon appears elongated probably because it’s rotating more slowly than the Alpha primary.
Meanwhile, the up and down direction or y-axis in the images shows the time delay in the reflected radar pulse on its return trip to the transmitter. Movement up and down indicates a change in 2004 BL86’s distance from the transmitter, and movement left to right indicates rotation. Brightness variations depend on the strength of the returned signal with more radar-reflective areas appearing brighter. The moon appears quite bright because – assuming it’s rotating more slowly – the total signal strength is concentrated in one small area compared to being spread out by the faster-spinning main body.
If that’s not enough to wrap your brain around, consider that any particular point in the image maps to multiple points on the real asteroid. That means no matter how oddly shaped 2004 BL86 is in real life, it appears round or oval in radar images. Only multiple observations over time can help us learn the true shape of the asteroid.
You’ll often notice that radar images of asteroids appear to be lighted from directly above or below. The brighter edge indicates the radar pulse is returning from the leading edge of the object, the region closest to the dish. The further down you go in the image, the farther away that part of the asteroid is from the radar and the darker it appears.
Imagine for a moment an asteroid that’s either not rotating or rotating with one of its poles pointed exactly toward Earth. In radar images it would appear as a vertical line!
Edit: The author of the above story says something potentially mixed up, IMO. He says, "The moon appears elongated probably because it’s rotating more slowly than the Alpha primary."
Asteroid that flew close by Earth 26th January has a moon
This GIF animation shows asteroid 2004 BL86, which safely flew past Earth on 26th January 2015. The 20 individual images used in the movie were generated from data collected by NASA’s Deep Space Network antenna at Goldstone, California yesterday. They show the primary body is approximately 1,100 feet (325 metres) across and has a small moon approximately 230 feet (70 metres) across. Image credit: NASA/JPL-Caltech Scientists working with NASA’s 230-foot-wide (70-metre) Deep Space Network antenna at Goldstone, California, have released the first radar images of asteroid 2004 BL86. The images show the asteroid, which made its closest approach yesterday at 8:19 am PST (4:19 pm BST) at a distance of about 745,000 miles (1.2 million kilometres, or 3.1 times the distance from Earth to the Moon), has its own small moon.
The 20 individual images used in the movie were generated from data collected at Goldstone on 26th January 2015. They show the primary body is approximately 1,100 feet (325 metres) across and has a small moon approximately 230 feet (70 metres) across. In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200 metres) or larger are a binary (the primary asteroid with a smaller asteroid moon orbiting it) or even triple systems (two moons). The resolution on the radar images is 13 feet (4 metres) per pixel.
The trajectory of asteroid 2004 BL86 is well understood. Monday’s flyby was the closest approach the asteroid will make to Earth for at least the next two centuries. It is also the closest a known asteroid this size will come to Earth until asteroid 1999 AN10 flies past our planet in 2027.
Asteroid 2004 BL86 was discovered on 30th January 2004, by the Lincoln Near-Earth Asteroid Research (LINEAR) survey in White Sands, New Mexico.
Radar is a powerful technique for studying an asteroid’s size, shape, rotation state, surface features and surface roughness, and for improving the calculation of asteroid orbits. Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than if radar observations weren’t available.
NASA places a high priority on tracking asteroids and protecting our home planet from them. In fact, the U.S. has the most robust and productive survey and detection program for discovering near-Earth objects (NEOs). To date, U.S. assets have discovered over 98 percent of the known NEOs.
In addition to the resources NASA puts into understanding asteroids, it also partners with other U.S. government agencies, university-based astronomers, and space science institutes across the country, often with grants, interagency transfers and other contracts from NASA, and also with international space agencies and institutions that are working to track and better understand these objects.
NASA’s Near-Earth Object Program at NASA Headquarters, Washington, manages and funds the search, study and monitoring of asteroids and comets whose orbits periodically bring them close to Earth. JPL manages the Near-Earth Object Program Office for NASA’s Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena.
In 2016, NASA will launch a robotic probe to one of the most potentially hazardous of the known NEOs. The OSIRIS-REx mission to asteroid (101955) Bennu will be a pathfinder for future spacecraft designed to perform reconnaissance on any newly discovered threatening objects. Aside from monitoring potential threats, the study of asteroids and comets enables a valuable opportunity to learn more about the origins of our solar system, the source of water on Earth, and even the origin of organic molecules that led to the development of life.
NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will provide overall mission management, systems engineering, and safety and mission assurance for OSIRIS-REx. Lockheed Martin Space Systems in Denver will build the spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages New Frontiers for the agency’s Science Mission Directorate in Washington.
NASA also continues to advance the journey to Mars through progress on the Asteroid Redirect Mission (ARM), which will test a number of new capabilities needed for future human expeditions to deep space, including to Mars. This includes advanced Solar Electric Propulsion &mdash an efficient way to move heavy cargo using solar power, which could help pre-position cargo for future human missions to the Red Planet. As part of ARM, a robotic spacecraft will rendezvous with a near-Earth asteroid and redirect an asteroid mass to a stable orbit around the moon. Astronauts will explore the asteroid mass in the 2020’s, helping test modern spaceflight capabilities like new spacesuits and sample return techniques. Astronauts at NASA’s Johnson Space Center in Houston have already begun to practice the capabilities needed for the mission.
Challenges postponing the first asteroid mining mission:
The first mission will not be profitable
Due to the amount of technology development and upfront capital expenditure, it's unrealistic for companies or investors to expect a quick return-on-investment. We're better off embracing that reality rather than willfully ignoring it. Even so, designing the mission with long-term profitability and multiple branches of resource extraction would go a long way towards convincing a government agency or billionaire investor to finance it. This will help to secure a future where the second/third/fourth missions are profitable and economically sustainable going forward.
On-site extraction is complex with many "unknown unknowns"
Nearly all concepts for asteroid mining involve sending the processing facility to the asteroid target and refining a certain resource on-site. This is the best in terms of minimizing return payloads for use in cislunar space and setting up infrastructure for long-term operations. Manufacturing your own fuel for the return trip also helps get more mass back. That is, assuming you find it in the expected concentration and the materials processing hardware doesn't fail due to an unforeseen issue.
However, this introduces a disproportionate amount of operational risk. On one hand, there may be problems of structural integrity and dust environment, which you might not discover until you began to excavate large amounts of material. On another hand, the issue of grappling or anchoring any smaller-than-asteroid spacecraft to perform such extraction would require very extensive engineering R&D which very likely could not be thoroughly tested in an operational environment prior to use. Doing this autonomously adds an additional layer of complexity between software and hardware systems.
Sending reconnaisance spacecraft extends timelines
To develop this level of sophisticated and autonomous mining technology for a single high-stakes mission with reasonable expectations of success, you would almost certainly need to pare down this risk by sending reconnaissance spacecraft to perform an in-situ assessment.
Every asteroid science mission has yielded new questions regarding the science and understanding of asteroids. The two asteroid sample return missions currently underway are having to problem-solve through unexpected hazards. Asteroid Ryugu's surface is devoid of regolith and littered with boulders, while asteroid Bennu is mysteriously ejecting particles.
The surface of Ryugu was not what we expected. So our sampler team had to conduct an experiment to check we could still gather material from the asteroid surface when we attempt #haya2_TD touchdown this Friday! https://t.co/bCzvW2gwSr pic.twitter.com/XxJXETKB6N&mdash [email protected] (@haya2e_jaxa) February 18, 2019
Each reconaissance mission costs money and time, reducing the profitability of the full-scale operation and further lengthening the financing timeline for return-on-investment. It's difficult to play such a waiting game with someone else's money.
Reconaissance would theoretically be able to confirm the particle size distribution, homogeneity, and chemical composition of the surface and subsurface. It may be able to rule out the physical dangers and risks of proximity spacecraft operations, but the economic concerns are much more nuanced. Due to the complex nature of asteroid formation and reworking, such robotic rendezvous probe may still not sufficiently answer all the necessary questions to inform proper development of a full-scale mission to process the asteroid target for some prize material in economic quantities.
Put another way, the main reason for sending the reconaissance mission to conduct in-situ analysis is to lower the risk of failure for the large-scale mining mission. The risk of failure can be drawn into two categories: operational risk and economic risk.
Operational risks - things that can kill your spacecraft
There may be unforeseen issue that would cause the entire mining mission to fail or would prompt a go/no go decision. Maybe this asteroid is spinning too fast or is a weird shape, making it difficult to model and perform safe proximity operations with a spacecraft. Maybe it's slightly too big for the capture enclosure or begins to shed materials in a dust cloud or tail.
Asteroid Bennu ejecting particles. Credit: NASA/Goddard/University of Arizona/Lockheed Martin
While these examples are real risks and possible scenarios, enough (but not all) operational risks can be pared down by a rigorous ground-based observing program prior to launch. There are no technical show-stoppers which would require the extra expenditure and timeline of conducting a reconaissance mission  …at least for the first mining mission.
Economic risks - things that can kill your bottom line
As part of this rigorous ground-based observation, spectra of the asteroid should confirm the presence of hydrated minerals via the 3-micron band  . This doesn't necessarily rule out the possibility that the target asteroid might be "drier" than expected. A reconaissance mission that observes the surface up close will likely clear up that ambiguity, but at what cost? If it's assumed that the first mission will not be profitable, the risk of a delayed timeline is more critical to the overall life cycle of the mission (and potential for getting canceled) than the risk of bringing back a "less than optimal" ore body. While in-situ measurements and "ground truth" are always good practice, the cost of a reconaissance probe is extremely high for what amounts to diminishing returns on the economic bottom-line.
Perhaps, this mission architecture is being over-engineered. Complexity can easily snowball into more complexity. To achieve a "Faster, Better, Cheaper"  outcome, a certain level of risk must be acceptable.
The hunt for asteroid impacts on the moon heats up with new observatory
Sometimes a flash in the night is actually an asteroid slamming into the moon.
Because such impacts offer valuable information about Earth's own barrage of space rocks, scientists have established programs that look for the brief bright flashes on the moon that represent lunar impacts. A new such telescope recently began operations, confirming observations of another telescope's 100th impact flash detection.
Having multiple eyes on the moon is valuable for scientists because other phenomena, like satellites passing overhead, can produce similar flashes in the data. But two observatories at different locations won't simultaneously see the same satellite: if both catch the same lunar flash at the same time, it's definitely real data.
The European Space Agency's Near-Earth Object Lunar Impacts and Optical Transients (NELIOTA) project, based at Kryoneri Observatory in Greece, does just this type of work. So far, the project has spent nearly 150 hours staring at the moon and observed 102 flashes. The instrument can also provide data that lets scientists estimate the temperature of the impact.
The milestone 100th observation came on March 1. And as scientists looked back over NELIOTA's data, they realized that a newcomer to the lunar impact patrol, the Sharjah Lunar Impact Observatory in the United Arab Emirates, had spotted the same flash. Scientists were able to compare images taken by the two observatories and line up lunar features, in addition to checking the timestamps of the flashes.
The double observation marks an important milestone for lunar impact surveillance efforts. "Cross detections like this are very useful as they rule out the possibility of a slow, bright satellite being misidentified as an impact flash," Detlef Koschny, co-manager of the Planetary Defense Office of the European Space Agency, said in a statement.
"While NELIOTA has other, less-direct means of excluding such events, we're excited to have more eyes on the moon, helping us to understand the rocky road our planet travels on," Koschny said. The Earth and moon are close enough &mdash on the scale of the solar system &mdash that both bodies should be hit by more or less the same hail of space rocks.
The flashes these observatories track come from just the sort of space rocks that regularly hit Earth without scientists being able to spot them: rocks that weigh less than 3.5 ounces (100 grams) and are less than 2 inches (5 centimeters) across, according to the statement. Rocks that small don't make it very far into Earth's thick atmosphere before burning away.
But the moon has no such atmosphere, so the same size rock can hit the surface &mdash pretty flashy.
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If we look at the typical speed of an asteroid that hit Earth, it drops down to something like 20 km/s, which is Earth orbital speed. In essence Earth, and I expect Moon, acts like giant fly swatters with an overlay of own speed of impactor in relation to Sun as well as Earth gravity as bolide says.
Is asteroid 2016 HO3 a second moon?
Here’s a word about asteroid 2016 HO3 – first spotted earlier this year – which astronomers say is a “constant companion” of Earth.
That doesn’t mean it’s a second moon. It doesn’t orbit Earth it orbits the sun. But its orbit keeps it as companion to Earth, and it will remain so for centuries to come. What’s more, as it orbits the sun, this asteroid appears to circle around Earth as well. That’s why the astronomers at NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California wrote about the object:
It is too distant to be considered a true satellite of our planet, but it is the best and most stable example to date of a near-Earth companion, or ‘quasi-satellite.’
Paul Chodas, manager of the Center for NEO Studies said:
Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth.
One other asteroid — 2003 YN107 — followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity.
This new asteroid is much more locked onto us. Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth’s companion for centuries to come.
Image of asteroid 2016 HO3 taken on June 10, 2016 by Denise Hung and Dave Tholen of the University of Hawaii. The asteroid is the bright dot near the center. During this 5-minute exposure, the telescope tracked the slowly moving asteroid, making the background stars appear trailed.
The Pan-STARRS 1 asteroid survey telescope on Haleakala, Hawaii first spotted asteroid 2016 HO3 on April 27, 2016.
Since then, astronomers have learned that, in its yearly trek around the sun, the spends about half of the time closer to the sun than Earth and passes ahead of our planet, and about half of the time farther away, causing it to fall behind. Its orbit is also tilted a little, causing it to bob up and then down once each year through Earth’s orbital plane. The Center of NEO studies said:
In effect, this small asteroid is caught in a game of leap frog with Earth that will last for hundreds of years.
The asteroid’s orbit also undergoes a slow, back-and-forth twist over multiple decades. Paul Chodas explained:
The asteroid’s loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth’s gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon.
The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon.
In effect, this small asteroid is caught in a little dance with Earth.
The size of this object has not yet been firmly established, but it is likely larger than 120 feet (40 meters) and smaller than 300 feet (100 meters).
Animation of the discovery images of asteroid 2016 HO3, taken on April 27, 2016 by the Pan-STARRS NEO search program. Pan-STARRS is located on Haleakala, Maui, and run by the University of Hawaii’s Institute for Astronomy.
The Center for NEO Studies website has a list of recent and upcoming asteroid close approaches, as well as all other data on the orbits of known NEOs.
For asteroid news and updates, follow AsteroidWatch on Twitter.
Or subscribe to Minor Planet Daily from the International Astronomical Union. They’ve been doing an awesome job on daily updates about asteroid close approaches.
Bottom line: Is asteroid 2016 HO3 as second moon? It isn’t because it orbits the sun. But its orbit keeps it as a constant companion of Earth, and it’ll remain so for centuries to come.