How scientists went to an asteroid to sample the Sun

In the intervening years the capsule had visited Bennu, a small asteroid in an orbit that crosses Earth’s orbit, as part of a mission called OSIRIS REx. In 2020, the mission’s main spacecraft briefly landed on Bennu’s surface and loaded perhaps 140 grams of material into the capsule. It then returned to Earth’s vicinity, moved away from the capsule, and flew on to study another asteroid named Apophis. The capsule fell into the atmosphere like an incoming meteorite; It failed to deploy its parachute the way it was planned (thus keeping Dr. Lauretta guessing) but surfaced safe and sound.

On December 11, Dr. Lauretta provided the gathering with some preliminary results from her team’s analysis of the material. Perhaps the most significant was the negative. The sample was ancient. Although fragments of asteroids fall to Earth as meteorites every day, they are not protected from the heat of reentry or subsequent contamination at the surface. Bennu was a model.

This matters because asteroids like Bennu are the most primitive objects in the Solar System, remnants of a cloud of gas and dust that collapsed to form the Sun. It is believed that there has been hardly any change in them in billions of years. This means that the elements they contain are present in the same relative abundances as are found in the raw material of the young Sun and the rest of the Solar System. The Bennu sample is “the largest ancient deposit of this material on Earth,” Dr. Lauretta said. “In my opinion as a cosmochemist, this alone makes the entire mission worthwhile.”

There’s more to a sample than simply adding elemental abundance. The boulders seen on Bennu came in a variety of forms, some hummocky, some angular. The rock grains in the sample, despite being hundreds of times smaller, show similar variation in types, a peculiarity that may take some time to explain. Although the minerals in the sample are more or less the same as those observed by OSIRIS REx across the entire surface of the asteroid, some grains are coated with mysterious layers rich in magnesium, sodium and phosphate, with which Dr. Lauretta seems to have been taken. There are clearly years, maybe decades, more work left for him and his team to enjoy.

One consequence of that September morning, however, has already arrived. As the capsule passed through the sky, a fleet of eight high-flying balloons watched it pass, not by light, but by listening to very low-frequency sound, known as infrasound, produced by its shock wave. . Their instruments marked its passage as a double-bang, heard first directly, then second as it bounced off the desert floor below.

Why go to all this trouble to hear the incoming rock? Because infrasound is a tricky thing, and it is not always possible to know what one is hearing when listening to its strange rumble. The return from Bennu dedicated scientists to listening for a sound similar to that of an incoming meteorite. If they find such double bursts in their data they will know what they are hearing.

The ultimate goal of such research is to create a catalog of all types of infrasound signals, including those from different types of earthquakes, says Siddhartha Krishnamurthy of the Jet Propulsion Laboratory, the California-based center that does most of NASA’s planetary science. Are. The application of such catalogs can be on Earth as well as on Earth. For example, infrasound-equipped balloons floating in the upper atmosphere of Venus would have a chance to capture earthquakes occurring below them.

The ability to diagnose Venus-quakes remotely would be extremely helpful. Designing a seismometer capable of operating in the hellish conditions of Venus’s surface is a difficult task, so being able to hear what was going on in the planet’s crust from above the planet’s clouds would prove to be a boon. And getting the most out of it will require being able to recognize other sources of infrasound for what they are. The ability to recognize the distinctive “knock” of an incoming extraterrestrial body would thus be important. This will also help scientists estimate the background rate of meteorite impacts on Venus, which could prove interesting in itself.

No one is expecting a fleet of infrasound-sampling balloons to appear in the morning star sky any time soon. But all scientific observers know that a good opportunity to classify background noise should not be wasted. Plus, there’s something about turning a side-effect of one part of solar-system exploration into a testbed for another that adds to the appeal of the whole endeavor.

© 2023, The Economist Newspaper Limited. All rights reserved. From The Economist, published under license. Original content can be found at www.economist.com

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Published: Feb 16, 2024, 07:25 PM IST