Asteroids! Bennu and YR4 Make Headlines

Two separate news stories out of NASA have a common theme — asteroids.  One set of scientists released findings from analysis of samples from the asteroid Bennu returned by the OSIRIS-REx mission, while another detected an asteroid, 2024 YR4, that has a tiny chance of colliding with Earth eight years from now.

Planetary scientists are deeply interested in asteroids. Rocks left over from the formation of the solar system 4.5 billion years ago, asteroids hold secrets that may answer fundamental questions about the origin of life on Earth and whether there is life elsewhere in the solar system.

The 121.6 grams (4.29 ounces) of material returned from Bennu in October 2023 by NASA’s Origins, Spectral Interpretation, Resource Identification and Security–Regolith Explorer spacecraft, OSIRIS-REx, are doing just that. Teams led by NASA Goddard Space Flight Center and the Smithsonian and London Natural History Museums have just published results of their analysis in Nature and Nature Astronomy.

Their excitement was palpable during a NASA media telecon yesterday as they shared what they’ve learned so far. OSIRIS-REx, or O-Rex, was not a life-detection mission, but the samples do contain 14 of the 20 amino acids life on Earth uses to make proteins as well as all five nucleobases that store and transmit genetic instructions including how to arrange amino acids into proteins. While the samples don’t show any evidence that life developed on Bennu, NASA concludes they suggest the conditions for life “were widespread across the early solar system.”

One surprise was the amount of ammonia in the samples, 100 times more than in soils on Earth. Ammonia is another building block of life. Nicky Fox, head of NASA’s Science Mission Directorate, explained amino acids and ammonia have been found in other extraterrestrial rocks, but finding them in these pristine samples that haven’t been contaminated by Earth’s atmosphere or surface “supports the theory that asteroids like that were among the sources that delivered water and chemical building blocks of life to Earth … so this is a groundbreaking discovery.”

Another surprise was the chirality of the amino acids. Danny Glavin, senior scientist for sample return at NASA Goddard, explained all life on Earth has 60 percent or more left-handed chirality. Scientists have also observed left handed chirality in meteorites — the remnants of asteroids that land on Earth — and therefore expected it in the Bennu samples. Instead, they are racemic, meaning equally left and right handed. He admitted he was “a little disillusioned or disappointed [because] I felt like this invalidated 20 years of research,” but “this is exactly why we explore.”

These results are from investigating only a small fraction of the material that came back — 0.06 percent. Scientists from around the world continue to study other samples, but NASA is setting aside 70 percent for later analysis including 7.5 grams (0.26 ounces) that will be put into a “deep freeze” container that won’t be opened for 50 years. By keeping them pristine, new discoveries may be made using whatever technologies emerge decades from now. NASA did the same with the lunar samples brought back by the Apollo crews.

As fascinating as asteroids are from a scientific standpoint, they also pose risks. Near Earth Objects (NEOs), which include asteroids and comets, can literally have Earth-shattering consequences. The extinction of the dinosaurs has been traced to such a collision 66 million years ago when an asteroid about 1 kilometer (o.6 miles) in diameter caused debris to billow up high in the atmosphere, blocking sunlight and altering the climate. Smaller asteroids can also have a considerable effect.  A 20-meter (66-foot) wide asteroid exploded over Chelyabinsk, Russia in 2013, injuring more than 1,000 people with flying glass from shattered windows.

Planetary defense scientists locate and track asteroids to determine if they might pose a threat to Earth. They just found one.

Using the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Chile, astronomers detected asteroid 2024 YR4 on December 27 and it rose on NASA’s automated Sentry risk list on December 31.

That list is for Near Earth Asteroids (NEAs) that have a “non-zero probability” of colliding with Earth.

NASA estimates there is only about one percent chance of that happening with YR4, but “no other known large asteroids have an impact probability above 1%.”

December 22, 2032 is the date it would arrive. Planetary defense specialists will be making additional observations and NASA points out the likelihood of it impacting Earth could go down as more data is collected.

With a diameter between 130-300 feet (40-91 meters), YR4 is pretty big in terms of the damage it could cause.  Lindley Johnson, NASA Planetary Defense Officer Emeritus, told SpacePolicyOnline.com that at “the low end of the scale (40 – 60 meters) it would be a “Tunguska-type” impact where over 2,000 square kilometers of forest were destroyed.  A larger size would of course be more devastating were it to impact on a landmass.”

The Tunguska event took place in 1908 over Siberia.

Two international groups monitor asteroids: the International Asteroid Warning Network (IAWN) chaired by NASA and the Space Mission Planning Advisory Group (SMPAG) chaired by ESA.

ESA estimates the probability of impact at 1.2 percent, but, like NASA, notes that “an asteroid’s impact probability often rises at first before quickly dropping to zero after additional observations.”  They are actively tracking YR4 although it will become unobservable in a few months as it moves behind the Sun.

SMPAG was established to prepare an international response to a threat from a NEA.  Johnson said if YR4 maintains its status as a risk next week, “SMPAG will discuss plans for activation at its meeting on the margins of the UN COPUOS Scientific and Technical Subcommittee,” referring to the U.N. Committee on Peaceful Uses of Outer Space which is holding the annual meeting of that subcommittee from February 3-14 in Vienna, Austria.

He added that calculations of the orbit are updated daily and published on the websites of NASA’s Center for Near-Earth Object Studies (CNEOS) and ESA’s Near Earth Object Coordination Centre (NEOCC).

NASA’s Planetary Defense Coordination Office (PDCO) is responsible for notifying the White House Office of Science and Technology Policy (OSTP) and other agencies of NEA threats in accordance with the U.S. National Preparedness Strategy and Action Plan for Near Earth Object Hazards and Planetary Defense. Johnson, who headed PDCO for many years, confirmed that the appropriate notifications have been made. He is now Planetary Defense Officer (PDO) Emeritus and Kelly Fast is Acting PDO.