FAS Astronomers Blog. Volume 32. Number 11.
Although, it really didn’t count as an official moon, a small object entered into a temporary orbit about the Earth and was called “the Earth’s second moon.” Asteroid 2024 PT5 was captured by the Earth’s gravity on September 26, 2024. It stayed around for a couple of months before leaving on November 25, 2024. At 32 feet wide, it probably would have gone unnoticed by most of us, except for the wide press coverage it has received over the last few months.
There have been a few other references to an “Earth’s second moon.” According to the folks at Wikipedia, the Earth has captured two other “second moons”, 2006 RH120 (2006 to 2007) and 2020 CD3 (2018 to 2020).
The Earth also has “quasi-satellites” – so named because they appear to be orbiting the Earth, while they are actually orbiting the Sun. Earlier this year (2024), object 2016 HO3 Kamo’oalewa was discovered and fell into this category. Last year (2023) object 2023 FW13 was also found. Tanya Hill, in the Conversation, notes five others: 2003 YB107, 2004 GU9, 2006 FV35, 2013 LX28, and 2014 OL339.
Back in 1997, object 3753 Cruithne was discovered following the Earth in its orbit around the Sun. It does (sort of) orbit the Earth in a long “horseshoe orbit” lasting 770 years. Cruithne wasn’t discovered until 1986 and its orbit was first tracked in 1997. At only three miles in diameter and a closest approach of 7 1/2 million miles, it isn’t something you will spot in the night sky or even through a telescope.
In addition to all these “moons,” there are several asteroids that follow orbits, which from time to time, come close to the Earth. They fall into the category of Near-Earth objects – those that cross the Earth’s orbit and, for some, pass close to the Earth. Every once in a while one will come close enough that we will hear about it in the press. However, don’t worry, You Don’t Need to Duck – the folks at NASA are keeping an eye out for these.
Selected Sources and Further Reading
- Asa Stahl. “Earth’s quasi-moons, minimoons, and ghost moons.” The Planetary Society. May 21, 2024.
- Tanya Hill. “Companions of Earth: minimoons, quasi-satellites and horseshoes.” The Conversation. August 10, 2016.
Selected Sources and Further Reading (Asteroid 2024 PT5 and Others)
- Madz Dizon. “Earth’s ‘2nd Moon’ Escapes Orbit, Starts Long Journey Around the Sun—Will It Ever Return?” The Science Times. November 28, 2024.
- Robert Lea. “Earth’s mini-moon has finally departed. Will it ever return as a ‘second moon?’” space.com. November 26, 2024.
- Jamie Carter. “Updated: Why Earth Now Has A ‘Second Moon’ — But Only For 57 Days.” Forbes. October 9, 2024.
- Maddie Molloy. “Earth to briefly gain second ‘moon’, scientists say.” BBC. September 25, 2024.
- Arianna Johnson. “Temporary ‘Mini-Moon’ Will Begin To Orbit Earth Next Week: What To Know.” Forbes. September 19, 2024.
- Eric Ralls. “It’s official: Earth now has two moons.” Earth.com.
- Tom Howarth. “Say Goodbye to the Earth’s Second Moon As It Leaves Before Thanksgiving.” Newsweek. November 25, 2024.
- Samir Sebti. “Earth’s second moon confirmed : Scientists discover new natural satellite orbiting our planet.” MSNBC. November 17, 2024.
- Ashley Strickland. “A space rock is about to become Earth’s new ‘mini-moon’.” CNN. September 20, 2024.
- Rebbeca Schneid. “Earth Is Temporarily Getting a Second ‘Moon’.” Time Magazine. September 18, 2024.
- Wikipedia contributors. “Claimed moons of Earth.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 5 Dec. 2024. Web. 14 Dec. 2024.
Selected Sources and Further Reading (Quasi-Moons)
- Jamie Carter. “Earth’s New ‘Second Moon’ Is As Big As The Statue Of Liberty—And Scientists Just Found Its Origin.” Forbes. April 27, 2024.
- Kiley Price. “New ‘quasi-moon’ discovered near Earth has been traveling alongside our planet since 100 BC.” Live Science. May 31, 2023.
- Kiley Price. “Newfound ‘Quasi-Moon’ Has Been Earth’s Fellow Traveler for Thousands of Years.” Scientific American. June 2, 2023.
- Maris Fessenden. “Bet You Didn’t Know About the Earth’s ‘Second Moon’.” Smithsonian Magazine. March 3, 2015.
Selected Sources and Further Reading (3753 Curithne)
- “Cruithne: Earth’s Second Moon?” Star Walk 2. July 12, 2024.
- Duncan Forgan, University of St. Andrews. “3753 Cruithne: The ‘Second Moon’ You Didn’t Know Earth Had.” Discover Magazine. December 1, 2022.
- Ethan Siegel. “Ask Ethan: Does Earth Really Have A Second Moon?” Forbes. June 26, 2016.
- Duncan Forgan. “Earth’s other ‘moon’ and its crazy orbit could reveal mysteries of the solar system.” The Conversation. February 25, 2015.
- “Meet ‘3753 Cruithne’: The ‘Second Moon’ You Didn’t Know Earth Had.” Physics-Astronomy.com. April 21, 2023.
- “Meet ‘3753 Cruithne’: The ‘Second Moon’ You Didn’t Know Earth Had.” Amazing Astronomy/YouTube. April 21, 2023.
Selected Sources and Further Reading (Near-Earth Asteroids)
- “Small Asteroid Is Earth’s Constant Companion.” NASA/JPL-Caltech. June 15, 2015.
- “NASA’s ‘Eyes on Asteroids’ Reveals Our Near-Earth Object Neighborhood.” NASA. December 10, 2021.
- “Asteroid Watch.” NASA.
- “Next Five Asteroid Approaches.” NASA Asteroid Watch.
- “Eyes on Asteroids. NASA Asteroid Watch.
- “You Don’t Need to Duck.” FAS Astronomers Blog. March 2024.
Technical Reading
- Carlos de la Fuente Marcos and Raúl de la Fuente Marcos. “A Two-month Mini-moon: 2024 PT5 Captured by Earth from September to November.” Research Notes of the AAS. Volume 8. Number 9. DOI 10.3847/2515-5172/ad781f. September 2024.
- T. Kwiatkowski, et. al. “Photometry of 2006 RH120: an asteroid temporary captured into a geocentric orbit⋆” DOI: 10.1051/0004-6361:200810965. Astronomy & Astrophysics. Volume 495. Pages 967–974. September 15, 2008.
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