At least one interstellar object (ISO) has likely crashed into Earth’s moon over the eons, a new paper suggests.
The moonwhich is filled with thousands of craters, is therefore a good hunting ground for objects originating in interstellar space, suggest the authors through statistics and simulations.
“Given the number of ISOs that we expect to encounter in the solar system, there are probably a few craters that have been formed by very high speed ISOs throughout the solar system, and there is probably one or two on the moon,” lead author Sam Cabot, a Ph.D. candidate at Yale University, told Space.com.
That said, the challenge is to find such a crater in the first place.
Related: Interstellar comet Borisov shines in incredible new Hubble photos
ISOs are comets or asteroids that have appeared beyond the borders of our solar system. Only two have been confirmed so far: ‘Oumuamua and Borisov. The new study suggests that we could learn more about the composition of these enigmatic objects if we could locate a crater on the moon formed by an interstellar impact.
Decades of observations of our large nearest neighbor, particularly with NASA’s Lunar Reconnaissance Orbiter, have provided high-definition maps that will be used for NASA’s Artemis program. The Artemis program aims to land humans on the moon later in the 2020s, if all goes according to plan.
That said, maps can only provide a limited amount of information about the craters that are imaged, the authors say. The challenge is that the maps provide little spectroscopic information about the composition of the craters. While some analysis can be done from orbit, the authors say it will likely take “ground truth” to determine if a crater actually formed from an ISO, Cabot said.
Related: Stunning photos of the moon taken by NASA’s Lunar Reconnaissance Orbiter
Predicting what the astronauts might find will be difficult, Cabot added, because the two ISOs already spotted are quite different from each other. Borisov is most similar to other solar system objects we know of; however, astronomers were surprised by the amount of carbon monoxide present in its composition, he said. ‘Oumuamua is even more enigmatic, he says, because there is no “satisfactory theory” that fully explains its composition.
Something was gassing off ‘Oumuamua’s surface and causing it to accelerate as it left our solar system for interstellar space, Cabot explained.
“The dilemma,” he continued, “is that we in the community have been observing with space telescopes, looking for the typical gases that you would expect to see evaporate from the surface that are in astronomical objects. None of them have been detected with confidence.”
Since astronomers haven’t been able to find typical outgassing products such as water, they instead believe the object has unique types of volatiles on its surface, Cabot said. (Volatiles are chemical elements and compounds that vaporize relatively easily.) To better understand what ISOs are made of more generally, the moon may present a location to gather concrete evidence, he added.
Related: Photographers capture ‘ridiculously detailed image’ of moon for NASA’s Artemis 1 launch
Even better, there could be boots on the lunar surface relatively soon. Provided funding and technology development for the Artemis program proceeds as planned, humans can search for the sources of craters in their landing zone.
The challenge, however, is that there’s no way to predict exactly where an ISO may have landed. Moreover, human excursions will be limited, for the time being, to the south pole of the moon; it’s where NASA and other space agencies hope to place their astronauts in the near future.
Nevertheless, Cabot said, human missions “provide us with many opportunities for the characterization of regoliths, [meaning] understand the composition of the lunar soil and try to answer questions about the early solar system.”
Related: How did the solar system form?
The little we know about ISOs suggests a strong hypothesis about how different these craters might be, he said. ISOs tend to move at higher speeds than other objects in our solar system. This is because objects that are bound to the sun have a kind of “speed limit” due to their confinement by the sun’s gravity.
“ISOs, which circulate freely throughout the galaxy, can enter the solar system at much higher speeds,” Cabot said. “So that was the premise of our paper: to investigate telltale signatures of very high velocity impacts.”
The astronomers chose the cut-off speed of 225,000 mph (360,000 km/h) because it is extremely rare for objects in the solar system to reach speeds close to this speed. The authors suggest that the signs of melting at the impact site may be higher at this increased velocity, although the composition of the melt depends on the composition of the rock in the area.
What’s needed next, Cabot said, is “a widespread characterization of lunar regolith, which we hope to see with Artemis.” The challenge, he continued, is that astronauts and their equipment will need to figure out how to process large volumes of the moon’s regolith to make a meaningful comparison with what an ISO may contain.
Related: NASA’s Artemis 1 lunar mission explained in photos
Some of NASA’s future robotic landing missions could serve as trials for large-scale treatment of regoliths. NASA has a program called Commercial Lunar Payload Services (CLPS), which aims to put private landers and payloads on the moon in support of Artemis missions. A selection of these payloads might be able to handle regolith as a secondary target compared to other scientific explorations, Cabot said.
In the meantime, the authors, along with the rest of the astronomical community, are still on the hunt for other ISOs through powerful wide-field telescopes. And this research will be stimulated in the near future when instruments such as the Vera C. Rubin Observatory come online.
An article based on the research has been published in the Planetary Science Journal (opens in a new tab). A preprinted version is available on Arxiv. (opens in a new tab)
#Interstellar #objects #crashed #moon