Hubble reveals new details about alien comet 3I/ATLAS
Confirmed as an alien comet, new observations have given us a much better idea of how large this interstellar object actually is.
Hubble has captured the sharpest images to date of interstellar object 3I/ATLAS, revealing new details about this icy alien traveller.
The discovery of the third interstellar object passing through our solar system has the astronomy community fairly excited. Given the limited amount of time we have to observe 3I/ATLAS before it leaves our solar system, never to be seen again, astronomers want to find out as much as they can about it, while they have a chance.
To this end, increasingly more powerful telescopes are being turned towards 3I/ATLAS. Ground-based observatories have been delivering images, so far, giving researchers a chance to make educated guesses at the nature of the object and how big it is.
On July 21, astronomers got their first look at 3I/ATLAS using the Hubble Space Telescope.
Hubble's first image of Comet 3I/ATLAS. The streaks in the background are distant stars, drawn out into lines as the telescope tracked the moving object. According to NASA, a blue filter was used for these observations. (Image: NASA, ESA, David Jewitt (UCLA); Image Processing: Joseph DePasquale (STScI))
With 3I/ATLAS currently surrounded by a cloud of dust, ice, and gas (its 'coma'), the solid nucleus of the comet cannot be seen, even by Hubble.
However, these observations give astronomers a better estimate of the size of this alien object, simply by comparing what they're seeing with the behaviour of 'home grown' comets.
From ground observatories, based on its brightness, the original best estimate for the size of its nucleus was anywhere from 10-20 kilometres in diameter. New data from Hubble has significantly reduced that, putting an upper limit on the comet's size of 5.6 kilometres wide.
That's still substantially larger than both 2I/Borisov and 1I/'Oumuamua, which were estimated at being roughly 500 metres wide and 100 metres wide, respectively. Still, the researchers who took the Hubble observations believe it's possible 3I/ATLAS's nucleus could be as small as just 320 metres across.
Hubble's view of 3I/ATLAS. The comet is travelling from left to right in this field of view, with the Sun generally located off the right edge of the image. (Image: NASA, ESA, David Jewitt (UCLA); Image Processing: Joseph DePasquale (STScI))
The image captured by Hubble also reveals more detail, confirming 3I/ATLAS's cometary nature.
As seen above, the solid nucleus is located within the bright region on the left side of the fuzzy 'teardrop'. The diffuse region on the right appears to be a plume of dust being ejected from it, as sunlight warms the nucleus' surface.
Comets produce tails of dust and ionized gas, which both generally point away from the Sun. However, this kind of dust plume being generated in the direction of the Sun is apparently common in comets when they are farther out in space and first begin to feel the Sun's heat.
Additionally, according to NASA, the researchers report seeing the hints of a dust tail streaming away from the nucleus.
We still have roughly a month before most telescopes will lose sight of comet 3I/ATLAS as it passes around the other side of the Sun. At that time, orbiters around Mars might get a better look. Then, starting in early December, astronomers will pick up observations of it again, and have at least until early 2026 before it gets too far away to see.
"Observations from other NASA missions including the James Webb Space Telescope, TESS (Transiting Exoplanet Survey Satellite), and the Neil Gehrels Swift Observatory, as well as NASA’s partnership with the W.M. Keck Observatory, will help further refine our knowledge about the comet, including its chemical makeup," says NASA.