# Today I learned about mini-moons **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [September 20, 2024, 9:54am UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510 "2024-09-20T09:54:27Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Love\_Rhombus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/love_rhombus/32/10694_2.png) [@Love\_Rhombus](https://boards.straightdope.com/u/Love_Rhombus)\ **Post date:** [September 20, 2024, 9:54am UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/1 "2024-09-20T09:54:27Z")
Apparently we get one every so often, and then they leave a short time later in a sort of astronomical summer fling. Pretty neat. If we did get a permanent new moon, I wonder what it would be called? Probably “Moony McMoonface.” 🙄 > **[Earth will get a second "mini-moon" for 2 months this year](https://www.cbsnews.com/news/earth-second-mini-moon-2024/)** > > The asteroid was discovered in August and is set to become a mini-moon, spinning around Earth in a horseshoe shape for about two months. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [September 20, 2024, 11:37am UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/2 "2024-09-20T11:37:56Z")
It’s not really a moon of Earth as it is actually in a resonant co-orbital relationship with the Sun but [3753 Cruithne](https://physics.uwo.ca/~pwiegert/3753/3753.html) is the closest thing we have to a quasi-permanent second moon. Stranger ---
**Author:** ![Balance](https://avatars.discourse-cdn.com/v4/letter/b/ccd318/32.png) [@Balance](https://boards.straightdope.com/u/Balance)\ **Post date:** [September 20, 2024, 1:35pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/3 "2024-09-20T13:35:10Z")
Someone asked in a chat yesterday if the mini-moon would have a tidal effect. They were picturing something rather larger than a rock 36 feet across. (Not that that’s not an impressively large rock, but it’s rather less than the images “mini-moon” conjures.) Given that its size keeps getting compared to a city bus and the relative briefness of its visit, I propose calling it TART (Terra Area Rapid Transit). 😉 ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [September 20, 2024, 1:38pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/4 "2024-09-20T13:38:00Z")
> [@Stranger\_On\_A\_Train](#): > > It’s not really a moon of Earth as it is actually in a resonant co-orbital relationship with the Sun but [3753 Cruithne](https://physics.uwo.ca/~pwiegert/3753/3753.html) is the closest thing we have to a quasi-permanent second moon. I was fascinated when I learned about Cruithne several years ago, but it’s not unique. Several more Near-Resonant Near-Earth objects (NEOs) have been discovered in recent years: > [@](#): > > More near-[resonant](https://en.wikipedia.org/wiki/Orbital_resonance) [near-Earth objects](https://en.wikipedia.org/wiki/Near-Earth_object) (NEOs) have since been discovered. These include [54509 YORP](https://en.wikipedia.org/wiki/54509_YORP), [(85770) 1998 UP1](https://en.wikipedia.org/wiki/(85770)_1998_UP1), [2002 AA29](https://en.wikipedia.org/wiki/2002_AA29), and [2009 BD](https://en.wikipedia.org/wiki/2009_BD) which exist in resonant orbits similar to Cruithne’s. [(706765) 2010 TK7](https://en.wikipedia.org/wiki/(706765)_2010_TK7) is the first identified [Earth trojan](https://en.wikipedia.org/wiki/Earth_trojan) (out of only two known as of 2024). > **[3753 Cruithne](https://en.wikipedia.org/wiki/3753_Cruithne)** > > 3753 Cruithne is a Q-type, Aten asteroid in orbit around the Sun in 1:1 orbital resonance with Earth, making it a co-orbital object. It is an asteroid that, relative to Earth, orbits the Sun in a bean-shaped orbit that effectively describes a horseshoe, and that can change into a quasi-satellite orbit. Cruithne does not orbit Earth and at times it is on the other side of the Sun, placing Cruithne well outside of Earth's Hill sphere. Its orbit takes it near the orbit of Mercury and outside t The... ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [September 20, 2024, 1:46pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/5 "2024-09-20T13:46:16Z")
This ought to be of interest, too: > **[Claimed moons of Earth](https://en.wikipedia.org/wiki/Claimed_moons_of_Earth)** > > Claims of the existence of other moons of Earth—that is, of one or more natural satellites with relatively stable orbits of Earth, other than the Moon—have existed for some time. Several candidates have been proposed, but none have been confirmed. Since the 19th century, scientists have made genuine searches for more moons, but the possibility has also been the subject of a number of dubious non-scientific speculations as well as a number of likely hoaxes. > Although the Moon is Earth's only natur... ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [September 20, 2024, 1:53pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/6 "2024-09-20T13:53:35Z")
> [@Love\_Rhombus](#): > > [Earth will get a second "mini-moon" for 2 months this year - CBS News](https://www.cbsnews.com/news/earth-second-mini-moon-2024/) I have to quibble with that headline a little bit. This is not a second mini-moon. We have one moon-sized moon already. This new object will be the second moon, but the only mini moon. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [September 20, 2024, 2:03pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/7 "2024-09-20T14:03:53Z")
You mean it’s really a Moon of Unusual Size. ---
**Author:** ![gregorio](https://avatars.discourse-cdn.com/v4/letter/g/fbc32d/32.png) [@gregorio](https://boards.straightdope.com/u/gregorio)\ **Post date:** [September 20, 2024, 2:06pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/8 "2024-09-20T14:06:09Z")
**M** oon **O** f **U** nusual **S** iz **E** ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [September 20, 2024, 2:14pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/9 "2024-09-20T14:14:08Z")
Deimos is about 6.2 km on average. Among Jupiter’s many moons, the miniest known so far is the smartly named S/2010 JII which is 1-2km. Of course there are likely to be many more mini-moons of Jupiter. For Saturn the current smallest is Aegaeon which is extremely elongated. Only about a half km thick. Strangely, the smallest moon of Pluto, Styx, is larger than any of the above. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [September 20, 2024, 2:14pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/10 "2024-09-20T14:14:26Z")
> [@Balance](#): > > a rock 36 feet across. (Not that that’s not an impressively large rock, but it’s rather less than the images “mini-moon” conjures.) 36 feet/11 meters isn’t especially impressive. The Chelyabinsk asteroid was around 18 meters, so the mini-moon is around 1/5th the mass of that. About the worst it could do is get [Mary Moon](https://m.youtube.com/watch?v=Qosk-UIQIjA) stuck in your head. ---
**Author:** ![Balance](https://avatars.discourse-cdn.com/v4/letter/b/ccd318/32.png) [@Balance](https://boards.straightdope.com/u/Balance)\ **Post date:** [September 20, 2024, 2:32pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/11 "2024-09-20T14:32:38Z")
In space, it’s not impressive. As a moon, it’s not impressive. It takes a lot to be impressive in space. If it were sitting on your lawn, though, it would make an impression. XD (Facetiousness aside, I was specifically pointing out the difference between human scale and space scales. To a human on Earth, a rock that size is a big rock. In space, it’s a dust mote against a darkened sky.) ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [September 20, 2024, 5:35pm UTC](https://boards.straightdope.com/t/today-i-learned-about-mini-moons/1007510/12 "2024-09-20T17:35:41Z")
Sadly, this fall’s mini-moon, named 2024 PT5, is too small and will be too far away to see, except with a really large telescope. That kind of diminishes general interest in it. It would be cool if something with an apparent size as big as the actual moon passed nearby. Actually, the Andromeda galaxy has an apparent size several times larger than the moon, but is too dim to see without a telescope. This is what it would look like if we could see it with the naked eye: [![](https://compote.slate.com/images/e2e949ab-e846-4db5-bb0c-8ab4c089fc7a.jpg) ](https://compote.slate.com/images/e2e949ab-e846-4db5-bb0c-8ab4c089fc7a.jpg)