‘The line gets blurrier’: asteroids and comets may be more similar than you think | Horizon: the European magazine for research and innovation
While the specimens may not be large, it turns out that these dust particles reform scientists’ conception of asteroids and comets and are enough to reconstruct entire scenes in the history of the solar system.
Asteroids and comets are primitive bodies left behind early in the formation of the solar system, so the more we can know about their makeup, the more we know about where they formed. Asteroids that formed in the same neighborhood as comets tend to be closer to them.
Trying to break down the asteroid-comet continuum and categorize how similar asteroids might be to comets is what Dr. Pierre Beck is doing in the SOLAR project at the University of France of Grenoble Alpes.
There are around a million officially registered asteroids and there should be many more, he explains.
“Traditionally, these objects have been considered the most primitive in the solar system. You can look at the ingredients and see what was there, how they were accreted, and how they formed long ago.
A similar primordial material that formed Earth or Mars has experienced geological activity and has been fundamentally changed by conditions such as heat, pressure, and erosion.
“The most primitive objects therefore do not come to Earth in the form of rocks, but in the form of dust,” he said. “While the expected (amount) of meteorites to arrive on Earth in a year may be 5 to 6 tonnes – for dust it is 40,000 tonnes.
Using samples of interplanetary dust collected from the highs of our stratosphere and micrometeorites from pristine places like Antarctica, Dr. Beck uses a new method of infrared spectroscopy combined with atomic force microscopes to examine their spectra and patterns. micrometric scale properties.
Like an archaeologist placing artifacts from an excavation site, he can then compare those findings to existing data from asteroids in space. “When you’re a geologist and you find a boulder, you have an outcrop and try to see the boulder in context,” Dr. Beck said.
“In the past, we thought asteroids were rocks, comets are icy. But now we see that there are comets that are almost inactive… and there are asteroids that are active.
Dr Jessica Agarwal, Technical University of Braunschweig, Germany
By using infrared laser light changes on samples that are only 10 to 20 microns in size, his team can for the first time select silicate minerals and organic compounds without using harsh chemicals that would disrupt the material. They’re also building larger sample models in the lab to refine what to look for to identify and classify asteroids and comets with ground-based telescopes.
What they found in the dust were complex organic polymers, rich in hydrocarbons and elements like nitrogen and oxygen or sometimes deuterium (heavy water).
“There is a big debate about how this extraterrestrial organic matter formed. One hypothesis is that the ice mixes were irradiated, but in this case different types of ice mixes should produce different types of organic material, ”said Dr. Beck.
Studying the chemical makeup of these samples should help him learn more about the origins of asteroids as well as the difference between D-type asteroids, dark and hard-to-detect bodies, some with icy interiors, which originate around Jupiter and beyond, and icy comets. .
“ If we understand this, it will tell us what the outer solar system is made of and more about the initial elements that entered the solar system. ”
Knowing where certain types of organic dust are located could even help future space probes.
“You can see some of these asteroids as a source of fuel,” he says. If there are any reduced organic compounds, he says, they could be used as an energy source.
The presence of such compounds in interplanetary dust is just one thing that makes scientists wonder if asteroids and comets are not necessarily so different after all. Dr Jessica Agarwal at CASTRA project thinks there may be some overlap for other reasons as well.
Using data from the European Space Agency’s Rosetta probe which studied comet 67P / Churyumov-Gerasimenko and astronomical telescopes, Dr Agarwal and his team at the Technical University of Braunschweig in Germany examined how comets and asteroids actively emit matter into space.
“We aim to better understand the processes that lead to changes in the surfaces and interiors of comets and asteroids,” she said. “We also hope to better understand their primitive nature, or what they were like 4.5 billion years ago.
Using data from several instruments aboard Rosetta, Dr Agarwal’s team were able to model the properties of cometary dust in the environment of comet 67P. They found that the dust particles could be loose aggregates of micron-sized silicate and sub-micron carbon components.
“We are also seeing huge boulder-sized material coming out of comet 67P, coming from specific places on the surface … a fountain of boulders,” Dr Agarwal explained.
Comets aren’t the only bodies that emit matter. Take the case of the asteroid 288P. A so-called active asteroid that emits dust, from a distance it looks like a comet with a dusty tail.
“The weird thing about 288P was that its kernel looked double… and in the end I thought, well maybe it’s a binary? Said Dr Agarwal. “ We had to wait a few years to re-observe it closely and then in 2016 we had more Hubble time and really saw that it was two components. ”
Their measurements determined that this first such asteroid to be observed is made up of two pieces of similar size, orbiting 100 kilometers from each other.
“We found it by chance. We don’t know if there are other systems like this that we don’t see, ”Dr Agarwal said.
They hypothesize that the asteroids have been irradiated by the sun and begin to spin, splitting in half when they spin too fast to hold together. The distance between the pair may be due to a jet of gas vaporizing from the surface that propelled a rock like a rocket. They’re still trying to figure out what’s causing the tail.
Scientists have long believed that asteroids evolve mainly in collisions, but it’s possible that for smaller asteroids, rapid rotation plays an equally important role.
Their research revealed a range of active asteroids, from those that have a one-time burst of activity (as if due to an impact), to those that repeatedly emit dust.
“There is a process that occurs more or less at random that triggers the eruption of dust clouds,” said Dr Agarwal, referring to the asteroids that emit repeated dust bursts. “ We think maybe it’s a quick spin that triggers landslides or something. ”
The upshot of all of this is that the distinction between comets and asteroids may be more of a spectrum than a hard division.
“The line is getting blurrier. In the past we thought asteroids were rocks, comets are icy. But now we see that there are comets that are almost inactive… and there are asteroids that are active. There is more of a transition between these two populations than we previously thought, ”said Dr Agarwal.
The research in this article was funded by the EU’s European Research Council. If you liked this article, consider sharing it on social media.