NASA’s Europa Clipper spacecraft has made valuable observations of the interstellar comet 3I/ATLAS, which in July became the third officially recognised interstellar object to cross into our Solar System.
The UVS instrument had a unique view of the interstellar comet during a period when Mars and Earth-based observations were impractical or impossible.
“We’re excited that this opportunity to view another target on the way to Jupiter was completely unexpected,” said Southwest Research Institute’s Dr Kurt Retherford, the principal investigator for Europa-UVS.
“Our observations have allowed for a unique and nuanced view of the 3I/ATLAS comet.”
What makes the Europa Clipper observations unique?
Within a week of the comet’s discovery, analysts at NASA’s Jet Propulsion Laboratory (JPL) identified its trajectory through the Solar System.
The Europa Clipper team quickly realised that their spacecraft could observe 3I/ATLAS in November, when Earth-based observations were largely blocked by the Sun’s position and Mars-based views were optimal.
During this time, Europa Clipper bridged the gap between Mars-based views from late September and Earth-based observations later.
With the comet’s trajectory passing between Europa Clipper and the Sun, its vantage point enabled the UVS team to view the comet from a unique perspective. Comets have both dust tails in the trailing direction and plasma tails in the direction away from the Sun.
Equipment onboard the JUICE mission reveals additional details about the interstellar comet
Europa-UVS’s unusual sunward viewpoint provided a unique downstream view of the comet’s two tails, largely from “behind” the tails, looking back towards the comet nucleus and coma (the cloud of gas surrounding it).
Additional data from the SwRI-led UVS instrument aboard ESA’s Jupiter Icy Moons Explorer (JUICE) will complement these insights, providing a more common anti-sunward view of 3I/ATLAS at the exact same time.
Dr Thomas Greathouse, co-deputy principal investigator of Europa-UVS, commented: “We’re hopeful that this new view, along with observations from Earth-based assets and other spacecraft, will help us to piece together a more complete understanding of the tails’ geometries.”
Discovering the comet’s composition
Europa-UVS detected oxygen, hydrogen and dust-related features, supporting the preponderance of data indicating that comet 3I/ATLAS underwent a period of high outgassing activity during the period just after its closest approach to the Sun.
“Europa-UVS is particularly adept at measuring fundamental transitions from atoms and molecules,” Retherford said. “We can see gases come off the comet, and water molecules break apart into hydrogen and oxygen atoms.”
This capability enables Europa Clipper to measure and analyse these atomic species with high precision, providing a deeper view into the comet’s processes and composition.
Why is this information crucial?
Dr Tracy Becker, co-deputy principal investigator of Europa-UVS, explained: “Understanding the composition of the interstellar comet and how readily these gases are emitted can give us a clearer view of the comet’s origin and how it may have evolved during transit from elsewhere in the galaxy to our Solar System.”
She concluded: “What are the chemical processes at play, and how can we unravel the comet’s origin in its own star system? Were those processes similar to how we believe our Solar System formed? Those are big questions.”
