Old Solar System Objects Surviving Dynamic Environments – Asteroids
In order to understand ‘how the solar system formed and evolved’, a long-standing question of astronomy, it is necessary to find an old celestial body that survived in a dynamic environment. These celestial bodies can mainly include comets and asteroids, and the difference between the two can be found mainly in ‘composition materials’ and ‘places where they spend a long time’.
First, asteroids are characterized by being composed mostly of rock and containing almost no volatile substances. They are largely classified into C-type (rich in “chondrite” carbonaceous), S-type (rich in “stony” silicate Si), and M-type (rich in “nickel-iron” metal) according to their composition and spectral type. Asteroids are classified as type C. These are mostly the first dusty disk of the solar system between the orbits of Mars and Jupiter, called the asteroid belt (mainly 2.2 to 3.3 au; 1 au is the distance from Earth to the Sun), stable points where the gravitational forces of Jupiter and the Sun balance, Lagrangian points L4 and L5 Dot dwells (Trojans; asteroids that exist about 60 degrees ahead of and behind Jupiter’s orbit), and there are also near-Earth asteroids (asteroids that are close to Earth’s orbit or actually pass through Earth’s orbit). . These are predicted to have been created by colliding celestial objects that did not become planets and planetesimals due to Jupiter’s gravity, creating small asteroids and dust particles.
At least 110 to 190 asteroids larger than 1 km in diameter are known to exist, and the number of smaller asteroids is much larger. The number of asteroids currently identified is 1,282,871 as of May 2023.
Old Solar System Objects Surviving Dynamic Environments – Comets
Next, comets are beautiful celestial objects that everyone likes. However, the actual appearance is unfortunately not going to be clean. It is a block of ice in which water, other volatile substances, and dust are frozen to the extent that it has the nickname of ‘dirty snow lump’. Comets are very difficult to observe with the unaided eye, but can be seen primarily through ephemeral atmospheric taillights composed of dust and gas that reflect sunlight as they approach the Sun in distant orbits. They usually contain water and small amounts of gases such as carbon dioxide, carbon monoxide and hydrogen oxide. In other words, a comet is a mixture of various types of ice, gas, silicates, metals, and dust.
For reference, these dust and gas are supplied from the center of the comet, called the nucleus. As it approaches the sun, the material in the nucleus is pushed back by particles flying from the sun, forming a blue ion tail and a dust tail made of silicate. will form Because of their small size and gravity, comets cannot hold their atmospheric tails for long and quickly dissipate. This is what makes a beautiful comet look.
By calculating the aphelion and perihelion of comets, it can be predicted that unlike asteroids, they are usually located far away from the sun. For example, the hometown of comets is the Kuiper Belt, the second dust disk in the solar system, or the Oort Cloud, which is an imaginary celestial body but is thought to contain more than trillions of comets. While orbiting the sun, they may change into short-period comets with shorter periods due to perturbations of the planets, or even disappear as they collide with the sun or are attracted to the planet’s gravitational field. Or it may be accelerated by the gravitational field and leave the solar system on the contrary.
A celestial body that has the properties of both an asteroid and a comet, an active asteroid (or main comet)
Then, is there no celestial body that has the properties of an asteroid and a comet at the same time? Objects called active asteroids (also called mainbelt comets or MBCs) have the same orbits as asteroids, but they appear to have comet-like visual characteristics. That is, celestial bodies that lose mass and show visual activity like comets, but whose orbits are surprisingly still in the orbit of Jupiter, like those of asteroids. The first active asteroid discovered was 7968 Elst-Pizarro (133P/Elst-Pizarro).
James Webb first discovers gas in an active asteroid/main comet
New discoveries from the James Webb Space Telescope are no longer surprising. Because it is a very sensitive and delicate telescope, observations often reveal new facts. This observation is also no exception.
ⓒ NASA, ESA, CSA, Mike Kelley (UMD), Henry Hsieh (PSI), Alyssa Pagan (STScI)
The data above highlights key similarities and differences between the spectrum of comet 238P/Read observed by NASA’s James Webb Space Telescope’s Near Infrared Spectrometer (NIRSpec) in 2022 and comet 103P/Hartley 2 observed by NASA’s Deep Impact mission in 2010. are showing First, the James Webb Space Telescope discovered water and gas in a rare comet located in the asteroid belt, active asteroid 238P/Read (discovered by astronomer Read). In particular, this is the first time that gas has been discovered around a comet in the asteroid belt, so it is considered a very important discovery.
Comet 238P/Read as seen by the James Webb Space Telescope © NASA, ESA, CSA, Mike Kelley (UMD), Henry Hsieh (PSI), Alyssa Pagan (STScI)
Dr. Michael Kelly, an astronomer at the University of Maryland who submitted an observation proposal and led the research, observed an object with (visual) characteristics of a comet in the asteroid belt in the past, but directly observed it and obtained spectral data. Explain that this is the first time that it has even been confirmed through. Dr. Kelly clearly identified the reason for the comet’s visual characteristics as ‘ice’. He argued that this would prove that water in the early solar system could be preserved in the asteroid belt in the form of ice, and explained why the above discovery was important.
An artist’s rendering showing the sublimation process in which water ice evaporates as main comet 238P/Read approaches the Sun ⓒ NASA, ESA
238P/Read The discovery of water vapor around comets gives great support to the theory that water, an essential component of life, was transported to Earth by comets. More interesting, however, is that comet 238P/Read did not contain the carbon dioxide that astronomers were expecting.
The main comet has the lowest ratio of water to carbon dioxide compared to other comets. © Kelly et al. 2023
The team explains that the absence of carbon dioxide is more surprising than the discovery of water, as carbon dioxide is usually predicted to account for about 10% of comet volatiles, according to theory.
Why was carbon dioxide not discovered?
The research team explains that there are two possibilities for why the above comet lacks carbon dioxide. First, it is possible that carbon dioxide was present during the formation of the comet, but it is possible that the carbon dioxide has already evaporated due to the nature of the comet being so close to the sun. If the above comet had existed in the asteroid belt for a long time, it could have evaporated slowly over billions of years because carbon dioxide evaporates more easily than water or ice. Also, secondly, the above comets could be comets formed in a region without carbon dioxide.
The spectral analysis, scattering process, and emission process after reabsorption of the main comet are recorded along with modeling prediction results. © Kelly et al. 2023
Comet 238P/Read observed by the James Webb Space Telescope © Kelley et al. 2023
The team will now conduct additional observations of active asteroids similar to Comet 238P/Read to confirm that they all have a similar composition. Through these small, faint objects in the asteroid belt, an age-old question of astronomy is increasingly moving toward an answer. This is because how water came to our planet Earth, represented by ‘life’, is still a big mystery that has not been solved. Understanding the distribution of ice and water in the solar system and their history will bring us closer to answering these questions.
Carbon dioxide was not found in the main comet, but it was found in Comet Hartley 2. © Kelly et al. 2023
- Nature provides an unedited version of the paper so that the research results can be checked early, so please understand that the message “accelerated article preview” is included in the figures. Manuscripts will undergo additional editing before final publication and may contain errors affecting the content.
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