Sending Juno to fly past interstellar comet 3I/Atlas?

3I/Atlas as seen by Hubble on July 21, 2025
Hubble’s most recent image of comet 3I/Atlas.
Click for original image.

It’s all clickbait! In what appears to be an example of silliness, a scientist, Avi Loeb of Harvard, has proposed repurposing the Jupiter orbiter Juno by using its remaining fuel and its main engine (unused since 2016 because it is feared it will explode if ignited) to send the spacecraft on a path allowing it to fly past the interstellar comet 3I/Atlas that is presently zipping through out solar system.

Not surprisingly, a politician, congresswoman Anna Paulina Luna (R-Florida), immediately latched onto this idea to garner her own publicity.

Loeb believes Juno, which is scheduled to plunge into Jupiter’s atmosphere at the end of its mission in Sept. 2025, could be repurposed. He suggests using its remaining fuel to redirect it toward 3I/ATLAS when the object passes within about 34 million miles of Jupiter in March 2026.

Florida Congresswoman Anna Paulina Luna has backed the proposal in a letter [pdf] to interim NASA Administrator Sean Duffy, urging the agency to explore extending Juno’s mission. “It is recommended that NASA conduct a study to assess how much fuel is left in Juno’s engine, and I support an extension of the Juno mission at least until mid-March 2026 at a cost of about $15M per 6 months from the current expiration date of mid-September 2025,” Luna wrote.

The problem with this idea is that it isn’t realistic. Juno really doesn’t have sufficient fuel, and as I mentioned, its main engine is suspect, so suspect that the science team decided in 2016 to never use it again, thus leaving Juno in a higher than planned orbit that required twice as much time at Jupiter to get the same work done.

There is also one more reason to doubt Loeb’s proposal. He has also proposed that 3I/Atlas is an alien probe, ignoring or dismissing the images and data that make if very clear that it is nothing more than a comet, albeit interstellar in origin. It appears therefore that he might very well represent the quality of scientists that Harvard is hiring these days.

Big sections break off of interstellar Comet 2I/Borisov

The uncertainty of science: New observations of the interstellar Comet 2I/Borisov as it exits our solar system indicate that large fragments have recently broken from it, and that the comet might possibly be on the verge of breaking up.

Astronomers have seen evidence of two fragments, but the data suggests these are relatively small compared to the entire comet. On the other hand,

Before perihelion, Jewitt’s analysis of Hubble images showed that Comet Borisov is much smaller than had been thought. The comet’s nucleus is not directly visible, but in the January 10th Astrophysical Journal Letters, Jewitt put its diameter between 0.4 and 1 kilometer. That’s small enough that solar vaporization of surface ices on the side facing the Sun could spin up its rotation beyond gravity’s ability to hold it together.

However, the comet’s size is tricky to estimate, as its surface appears to be emitting so much gas and dust that it obscures the nucleus. The fragment that Jewitt observed is about as bright as the comet itself, but because its surface is so icy and active, he thinks the fragment’s mass is less than 1% of the whole comet. That would make the split more like a side mirror dropping off a car than a car falling apart. Why the fragment split from the comet is unclear, but possibilities include thermal vaporization after new material was exposed, as well as the force from the comet’s spin if it’s spinning as fast as Jewitt suggests.

Whether the comet is about to break up remains unknown. Wouldn’t it be nice if someone was racing to put a mission together to visit it?

Scientists propose mission to interstellar comet Borisov

In a paper published on the Cornell arXIiv site for preprint science papers, scientists have posted a paper proposing sending an unmanned probe to the newly discovered interstellar Comet Borisov, arriving in 2045.

You can download the paper here. [pdf]

Their analysis found that we just missed the ideal and most efficient launch date using the Falcon Heavy. If it had launched in July 2018 a two-ton spacecraft could have reached Comet Borisov by next month.

The best alternative option is a launch in January 2030, flying past Jupiter, then the Sun, and arriving in 2045. Because of the mission’s close approach to the Sun to gain speed, the mission would require the type of shielding developed for the Parker Solar Probe. If the Space Launch System was used for launch, a six-ton spacecraft could be sent. With other available rockets the largest possible payload would be 3 kilograms (about 6 pounds), making the probe a cubesat. As they note,

Despite this very low mass, a CubeSat-scale spacecraft could be sent to the interstellar object. Existing interplanetary CubeSats (Mars Cube One) show that there is no principle obstacle against using such a small spacecraft to deep space.

In fact, having a decade and a half before launch guarantees that a cubesat will be able to do this job, because by 2030 the technology for using smallsats for this kind of planetary mission should be fully developed.

First high quality image of interstellar comet

Comet Borisov
Click for full image.

The Gemini Observatory on Mauna Kea has successfully taken the first high resolution image of comet C_2019 Q4, unofficially Comet Borisov (after its discoverer), the first interstellar comet ever discovered.

The image to right, cropped to post here, is that image. It clearly shows the growth of a coma and possible tail, indicating that as it is approaching the Sun it is releasing material from its surface.

Right now the comet is visually very close to the Sun, when looked at from the Earth, making observations difficult. As in the next few months it drops towards its closest approach of the Sun, and the Earth circles around in its own orbit, the viewing angle will improve.