Halfway between asteroids and comets, centaurs, space rocks that take their name from the famous mythological creatures half man and half horse, have abandoned their distant orbits, beyond Neptune, to migrate to the inner solar system, towards the which are heading at full speed. And the closer they are to the Sun, the more they resemble comets and the less like conventional asteroids.
Having remained for billions of years in the icy confines of our planetary system, centaurs treasure valuable data about their birth, information that is revealed as they slowly begin to thaw in this passing stage of their existence.
Now, an international team of astronomers has used the powers of the James Webb Space Telescope to observe 29P/Schwassmann-Wachmann 1, one of the most active and interesting objects in the outer solar system. The high degree of detail captured by the telescope allowed for the discovery of new, previously unknown jets of gas, which is helping to complete theories about how both the centaurs themselves and the planets formed.
Regular bursts
Centaurs, then, are ancient trans-Neptunian objects that now lie between the orbits of Neptune and Jupiter due to the subtle gravitational influences of the planets over the past few million years.
Because these small icy bodies are in an orbital transition phase, they are of greatest interest, and scientists are trying to understand their composition and the reasons that drive their degassing (the loss of ice found below the surface). Their unique mix of characteristics, in fact, makes centaurs true hybrids between the primordial icy bodies of the outer Solar System and evolved comets, which have already passed close to the Sun once or several times.
29P/Schwassmann-Wachmann 1 (29P for short) is an object known for its highly active, quasi-periodic outbursts. Its intensity varies every six to eight weeks, making it one of the most active objects in the outer solar system. But now astronomers, thanks to the NIRSpec (Near-Infrared Spectrograph) instrument on the James Webb Space Telescope, have just discovered a new carbon monoxide jet and several other carbon dioxide jets that have never been seen before and that provide new clues. on the nature of the centaur nucleus.
“Centaurs,” explains Sara Faggi, of NASA’s Goddard Space Flight Center in Greenbelt, and lead author of a study published in ‘Nature Astronomy‘- can be considered as the remains of the formation of our planetary system. Because they have been stored at very cold temperatures, they preserve information about volatile elements in the early stages of the Solar System. The James Webb telescope really opened the door to a resolution and sensitivity that has impressed us: when we first saw the data, we were excited. We had never seen anything like this.”
difficult to observe
The enormous distance at which centaurs are found has greatly limited astronomers’ observations. And in the case of 29 P so far the data showed a single jet pointing towards the Sun (and the Earth) composed of carbon monoxide (CO). James Webb also detected this jet head-on, but thanks to his extraordinary infrared capabilities he also located many other chemicals, such as water (H2O) and carbon dioxide (CO2), one of the main ways in which carbon is stored throughout the world. Solar system.
The images and data revealed by the telescope revealed, in fact, features never seen before: two CO2 jets emanating in the north and south directions, respectively, and a third CO jet pointing north. This was the first definitive detection of carbon dioxide in 29P.
Using data collected by Webb, the team created a 3D model of the jets to understand their orientation and origin. And they discovered that they were emitted from different regions of the centaur’s core, although Webb cannot resolve the core itself. The angles of the jets suggest the possibility that the core is an aggregate of distinct objects with different compositions; however, other scenarios cannot yet be excluded.
The mystery continues
The reasons for 29P’s sudden brightness increases and the mechanisms behind its outgassing activity through these jets, however, remain a mystery.
In the case of comets, scientists know that their jets are often powered by the outgassing of water. However, due to their location, centaurs are too cold for water ice to sublime (from solid to gas without passing through the liquid phase), meaning that the nature of their outgassing activity is not the same as that of comets.
“We only had time to look at this object once, like a snapshot in time,” explains Adam McKay, co-author of the study. I would like to observe Centauro 29P for a much longer period of time. Do the jets always have the same orientation? Is there perhaps another jet that ‘turns on’ at a different point in its rotation period? “Observing these jets over time would give us a much better idea of what is driving these bursts.”
Researchers are hopeful that as they continue to learn from 29P, they can apply the same techniques to other centaurs. Improving what is known about these objects can simultaneously improve our understanding of the formation and evolution of our Solar System.
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