New Images Reveal Interstellar Comet's Closest Earth Approach

Observing an Interstellar Comet

The Hubble Space Telescope and the Jupiter Icy Moons Explorer have captured new images of an interstellar comet as it approaches its closest point to Earth later this month. This comet, known as 3I/ATLAS, has fascinated astronomers because it originated outside our solar system yet was discovered traveling through our celestial neighborhood in July. Given that it is only the third interstellar object ever observed passing through our solar system, scientists have directed multiple missions to study it.

Observations have been crucial in helping researchers understand the comet’s path and even provide insights into its composition. The gases that sublimated from the comet during its closest approach to the sun in October have offered valuable clues about its makeup. Hubble was among the first to observe 3I/ATLAS in July shortly after its discovery, providing the most detailed view of the comet’s teardrop shape at the time.

Astronomers spotted 3I/ATLAS again on November 30, when it was 178 million miles (286 million kilometers) from Earth. Using the telescope’s Wide Field Camera 3 instrument, they captured a clearer image of the comet. Meanwhile, an image taken by the European Space Agency’s Jupiter Icy Moons Explorer, or Juice, mission en route to study Jupiter and its icy moons, shows intriguing activity around the comet.

Spotting Two Tails

The Juice mission aims to investigate the potential habitability of Jupiter’s three largest moons: Ganymede, Callisto, and Europa. These moons are believed to host subsurface oceans beneath their icy crusts, which could potentially support life. However, before Juice can begin its main mission, it must reach Jupiter. The mission launched in April 2023 and is expected to arrive at its destination in July 2031.

At the beginning of November, Juice was in a prime position to observe 3I/ATLAS from about 41 million miles (66 million kilometers) away from the comet. The spacecraft used five of its scientific instruments, along with its onboard Navigation Camera, or NavCam, to capture glimpses of the comet. Most of Juice’s data won’t arrive on Earth until February because the spacecraft is using its main antenna as a heat shield to protect it from the sun during its long journey to Jupiter. A smaller antenna is sending back data at a slower rate.

The Juice team didn’t want to wait that long, so they downloaded a quarter of a single image taken by NavCam. The image shows heat-driven activity on the comet during its close pass by the sun. The newly released image shows a coma, or a glowing halo of gas surrounding the comet, as well as two tails: a plasma tail composed of electrically charged gas, as well as a faint dust tail of solid particles being released.

Comets that originate in our solar system typically have both of these tails, as well as a hazy coma surrounding a solid core made of rock, gas, dust, and ice leftover from the formation of the sun, planets, or other celestial bodies. As comets approach stars like our sun, they heat up, forming tails of sublimating material that streak behind them.

Closest Approach to Earth

Comet 3I/ATLAS will come within 167 million miles (270 million kilometers) of Earth on December 19, but it will be on the other side of the sun and poses no risk to our planet. For reference, Earth is about 93 million miles (150 million kilometers) from the sun. The comet is expected to remain visible to telescopes and space missions for a few more months before exiting our solar system, according to NASA.

The rest of the Juice data from the comet’s flyby, expected between February 18 and 20, should include images from the spacecraft’s high-resolution optical camera, as well as composition and particle data that could provide more clues about where the interstellar object originated.