How Many Moons Does The Earth Have?

Depending on when you ask the question, the answer you’re thinking of may not be correct:

Earth has two moons, a group of scientists . One is that waxing and waning nightlight we all know and love. The other is a tiny asteroid, no bigger than a Smart Car, making huge doughnuts around Earth for a while before it zips off into the distance and is replaced by another.

That’s the scenario posited by the scientists in a paper published Dec. 20 in the planetary science journal ICARUS. The researchers argue that there is a space rock at least 1 meter (3.3 feet) wide orbiting Earth at any given time, though it’s not always the same rock.

In the scientists’ theoretical model, our planet’s gravity captures these asteroids as they pass near us on their way around the sun. When one is drawn in, it typically makes three irregularly shaped swings around Earth — sticking with us for about nine months — before hurtling on its way.

According to the researchers, surprisingly little attention has been paid to Earth’s natural satellites other than the moon, despite the fact that they’re sure to exist. “There are lots of asteroids in the solar system, so chances for the Earth to capture one at any time is, in a sense, not surprising,” said co-author Jeremie Vauballion, an astronomer at the Paris Observatory in France.


“Objects of this size are too faint to be detected when being at a distance of, say, a few lunar distances from the Earth,” Gravnik told Life’s Little Mysteries, a sister site to”When coming closer in during their orbit, they are moving too fast to be detected, because the limited amount of photons is spread over too many pixels.”

These limitations mean we don’t currently have a way of finding our second moons. But an observatory called the Large Synoptic Survey Telescope (LSST), planned to open in Chile in 2015, could change that.

“We hope that LSST will do something about this, but dedicated programs will without doubt be even better,” Vauballion said. “Statistic study is still needed to see where and how to look for them.”

NASA’s Spaceguard Survey tracks the paths of all near-Earth objects (NEOs) in Earth’s neighborhood that are larger than 0.6 miles (1 kilometer) in diameter, but the scientists are less concerned with bodies that are too small to pose a threat to Earth — as is the case when they’re just 1 meter wide.

But if our distant, noncommittal moons don’t threaten Earth, and are much too dim to act as nightlights, does it matter that they’re there at all?

According to astronomers, it does. Some researchers say it might be possible to go and get one of these temporary moons and bring it back to Earth for analysis.

“When found, such an asteroid will immediately raise the question whether or not we should go, and I’m ready to bet that many astronomers will argue that we definitely have to go!” Vaubaillon said in an email. “The reason is simple: What astronomers would not want to have a full and intact (unaltered by any physical process) piece of space rock? Meteorites are all altered because they go through our atmosphere. The only piece of asteroid we have comes from the Japanese Hayabusa mission (a few grams at the very most). The comet grains the Stardust mission got back from comet Wild 2 were all altered.”

H/T Rand Simberg

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Doug Mataconis
About Doug Mataconis
Doug Mataconis held a B.A. in Political Science from Rutgers University and J.D. from George Mason University School of Law. He joined the staff of OTB in May 2010 and contributed a staggering 16,483 posts before his retirement in January 2020. He passed far too young in July 2021.


  1. Hey Norm says:

    Randy Moss was fined $10K for pretending to moon GB Packers fans.

  2. If we’re extending the definition of moon to include NEOs, then the title of “second moon” belongs to Cruithne, a 5km asteroid discovered in 1986 that’s in a 1:1 resonant orbit with the earth, or TK7, a 300 meter asteroid discovered in 2010 that’s hanging out in Earth’s L4 Trojan point.

  3. I’d also like to nominate YORP, which is only 100m, on the grounds that YORP would be an awesome name for a moon.

  4. rodney dill says:

    @Hey Norm: I was at that game, but for me it was a moonless night.

  5. rodney dill says:


    How Many Moons Does The Earth Have?

    Does the Deathstar count?

  6. Rodney,

    ixnay on the eathday tarsay

  7. Just nutha ig'rant cracker says:

    Go to get an asteroid 1 meter or so wide. Now there’s a trillion or so dollars well spent,

  8. OzarkHillbilly says:

    @Just nutha ig’rant cracker:

    Go to get an asteroid 1 meter or so wide. Now there’s a trillion or so dollars well spent,

    I agree. Much better to just go and invade another Muslim country.

  9. jd says:

    @rodney dill: That’s no moon!

  10. G.A.Phillips says:

    Randy Moss was fined $10K for pretending to moon GB Packers fans.

    That’s good to know. I thought he was acting like he was wiping his a$$ on the goal post….