The Webb Telescope will drop everything to observe the next interstellar object

The James Webb Space Telescope is a multi-talented machine. He can peer through the dense dust of space, glimpse the stellar drama of distant galaxies, and even observe the first stars in the universe. But some of Webb’s most fascinating work will answer much closer questions, like the intriguing dilemma known as interstellar objects.

These objects – whether comets, asteroids, or alien artifacts maaaaaaaybe (depending on who you ask) – were born from another star, and they carry valuable data locked away in their gaseous coma and their frozen core.

Astronomers tracked two of these objects and gathered as much information as possible from ground-based and space-based telescopes during their short-lived journey through the solar system. But a planned study using Webb’s 6.5-meter mirror and an advanced suite of infrared cameras will paint an even clearer picture of these interstellar objects, their alien host stars, and how unique our own solar system is among billions of stars. stars that make up the Milky Way.

In 2019, Hubble was able to examine 2I/Borisov, but Webb was able to unlock the mysteries of the next interstellar objects. NASA, ESA and J. DePasquale (STScI)

What makes an interstellar object?

On October 19, 2017, the Pan-STARRS telescope in Maui, Hawaii spotted a strange object traversing the solar system. The object’s speed as well as its extreme eccentricity meant that it was not gravitationally bound to our Sun. This object, named ‘Oumuamua (meaning “messenger from afar who arrived first”), was the first interstellar object ever recorded – and what an object it was.

Described as “cigar-shaped”, Oumuamua’s length was 10 times its width, an extreme oddity among space objects, and astronomers initially classified this interstellar intruder as a comet. But because it didn’t have a coma, a sort of atmosphere around a comet caused by the sublimation of ice, NASA reclassified it as an asteroid – but that badminton nomenclature doesn’t stop there. .

As it exited the solar system, ‘Oumuamua unexpectedly accelerated past the Sun due to a cometary trait called “outgassing”. To make matters even more confusing, some astronomers believe Oumuamua is neither a comet nor an asteroid but rather some kind of “cosmic iceberg”.

Because it was only a quarter of a mile long, ‘Oumuamua was no longer visible to any telescope – terrestrial or orbital – as of January 2018. ‘Oumuamua is now estimated to be crossing Neptune’s orbit as it continues its journey towards the constellation Pegasus. Astronomers will never study this unique object again in a lifetime.

“Oumuamua, along with the discovery of the mostly normal rogue comet Borisov in 2019, are the only two interstellar objects ever recorded in our solar system. Because astronomers have no idea when the next interstellar object will cross the sky, what it will look like, or how long it will be observable, Webb could assemble comet and asteroid experts to be ready for whatever the galaxy launches us. .

And if ‘Oumuamua is any indication, they’ll need all the help they can get.

Animation of the unusual tumble of ‘Oumuamua. NASA/JPL-Caltech

A complex web of interstellar science

Earlier this month, NASA released the first images captured by the $10 billion Webb Telescope. One of the astronomers eagerly awaiting these images was Michael Kelley, a cometary scientist at the University of Maryland and a co-investigator on the telescope’s interstellar object proposal. Although his first glimpse of Webb’s potential lived up to the hype (his shot of the Carina Nebula is now his wallpaper), Kelley sees Webb as perfectly suited for the job.

“I like to call it a ‘comet science machine,'” Kelley says. Reverse. Indeed, Webb’s imaging and spectrographic capabilities will give astronomers like Kelley an extraordinary amount of detail, including whether this comet is interstellar or local.

Comets are primarily composed of three main ices – water, carbon dioxide and carbon monoxide – Webb’s Near Infrared Spectrograph (NIRSpec) will analyze the chemical composition of these ices simultaneously as they are slowly vaporized by the heat of the Sun. This gives astronomers clues as to where in its host system an interstellar object may have formed. Lots of water, for example, could mean the object has moved closer to its star because other ice requires cooler temperatures, Kelley said.

Using the Mid-Infrared Instrument (MIRI), Webb will also provide insight into the composition of the dust emanating from these bodies. The data it provides could support some of the biggest theories of how oceans formed or how life took root in our solar system.

“Carbon is a great molecule because it’s what sustains life,” Kelley says. “The idea is that comets and asteroids have brought carbon to the Earth’s surface…one of the things we’re looking for is this carbonaceous dust.”

Comets are like cosmic time capsules. Because they typically form within the confines of a star system, comets are often encased in ice, preserving the geology of their protoplanetary formation for billions of years.

Asteroids, on the other hand, are often subjected to warmer temperatures, causing them to melt or otherwise change. While scientists believe that comets make up the majority of interstellar objects (because comets are more frequently ejected), an interstellar asteroid isn’t ruled out.

Cristina Thomas is a planetary scientist at Northern Arizona University, a co-investigator on the Webb proposal, and an asteroid expert. While Kelley is interested in the chemistry of interstellar comets, Thomas focuses on what Webb might tell us about the solid surface of a possible interstellar asteroid.

“I think a lot of people think of asteroids as sort of monolithic, like Han Solo flying through an asteroid field,” Thomas said. Reverse. “They’re actually so incredibly different from each other in so many ways.”

Webb will be able to glimpse these differences using near and mid-infrared wavelengths and provide data on an asteroid’s silicates, mineral signatures, possible surface hydration, and composition of its surface – be it rocky or porous (like Bennu).

Because of Oumuamua’s asteroid-like characteristics, Thomas and his team used the cigar-shaped puzzle as a test case to determine what Webb will see if another interstellar asteroid arrives in our galactic neighborhood.

“With ‘Oumuamua, we haven’t had a lot of in-depth sightings. [With Webb], we’re going to get broad wavelength coverage – it’s going to tell us a lot about the object itself and it’s really going to allow for a comprehensive comparison,” says Thomas. “We could assume that other systems have similar core elements, but to actually see it will be really great.”

Artist’s impression of the Rubin Observatory. Todd Mason, Mason Productions Inc. / LSST Corporation

Waiting for Rubin

While Webb is ready to gaze upon the next interstellar object that crosses his path, one big hurdle remains – scientists must find one first.

While two have been discovered in the past seven years, Kelley believes a more reliable frequency of discovery is to spot an interstellar object every ten years. Fortunately, a new ground-based telescope perched on the ridge of Cerro Pachón in north-central Chile will change all that.

As part of its Legacy Survey of Space and Time (LSST), the Vera C. Rubin Observatory will map the solar system more accurately than ever before. The Hawaiian Pan-STARRS telescope discovered ‘Oumuamua with a 1.8 meter mirror. By comparison, Rubin is equipped with a mirror more than four times larger, which scientists believe could blow up the known number of objects in our solar system by a factor of 10 (or even more). And among them there could be a number of strange objects whose speed and eccentricity indicate interstellar origins.

“We need a new discovery to make this project work. It all depends on what is discovered,” Kelley says. “Borisov was easily observed for a long time. ‘Oumuamua had to be observed within a month.’

Because astronomers could spot an interstellar object at any time, this particular study is part of NASA’s Target of Opportunity program. This program allows teams studying time-sensitive phenomena, such as supernovae or interstellar objects, to interrupt Webb’s regular programming with as little as three days. This particular study falls under the category of “opportunity disruptive target,” meaning Webb could focus his gaze on an incoming interstellar object within two weeks of its discovery.

In the future, Webb’s data on interstellar objects could inform other, even more ambitious space missions, such as the European Space Agency’s Comet Interceptor. Launching in 2029, this spacecraft will be stationed at Lagrange Point 2 while waiting for an appetizing long-period comet or interstellar object to track and study. While telescopes are great, nothing compares to the science gathered on a space mission, which high-level science projects like Rosetta and Osiris-REx undoubtedly prove.

“Every time we send a spacecraft somewhere, we learn something completely new,” says Thomas. “But even though James Webb isn’t the same as sending a spacecraft, we’re still going to see so much more… It’s going to change the paradigm on how we think about these objects.”

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