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.

New Hubble observations of Comet 3I/Atlas refine its size

3I/Atlas as seen by Hubble on July 21, 2025
Click for original image.

Using the Hubble Space Telescope, astronomers have refined significantly the size of the interstellar object Comet 3I/Atlas as it zips through the solar system in its journey through the galaxy.

The image to the right, cropped and reduced to post here, is a Hubble image taken on July 21, 2025. The streaks are background stars.

Hubble’s observations allow astronomers to more accurately estimate the size of the comet’s solid, icy nucleus. The upper limit on the diameter of the nucleus is 3.5 miles (5.6 kilometers), though it could be as small as 1,000 feet (320 meters) across, researchers report. Though the Hubble images put tighter constraints on the size of the nucleus compared to previous ground-based estimates, the solid heart of the comet presently cannot be directly seen, even by Hubble.

…Hubble also captured a dust plume ejected from the Sun-warmed side of the comet, and the hint of a dust tail streaming away from the nucleus. Hubble’s data yields a dust-loss rate consistent with comets that are first detected around 300 million miles from the Sun. This behavior is much like the signature of previously seen Sun-bound comets originating within our solar system.

In other words, though this object comes from far outside our solar system, it so far appears to closely resemble comets from our own system. If confirmed, this fact is quite significant, as it suggests the formation of solar systems throughout the galaxy are likely to be relatively similar to our own.

Comet 67P/C-G at 126 miles

Comet 67P/C-G at 126 miles

The image above was taken by Rosetta on August 4 from only 126 miles (234 kilometers). Unlike earlier images, this image is raw, uncropped and unprocessed. All I have done is rescale it to fit on my webpage. As they explain at the link,

As you can see, the comet is not centred in the full-frame image. This is a result of the rendezvous burn conducted the previous day, which adjusted Rosetta’s trajectory towards the comet. This effect is corrected for in the commands sent to the spacecraft after the new orbit has been determined.

The science team also notes that beginning tomorrow, the comet will be close enough that they will no longer have to provide a cropped close-up using the navigation camera and that this uncropped raw version will be sufficient.

Rendezvous and orbital insertion on Wednesday!

The next great comet?

Amateur astronomer Jason Lewis sent me an email today describing how the amateur astronomy community is abuzz with the discovery of a new comet, presently dubbed C/2012 S1, that is due to make its dive around the Sun in late November 2013 and pass closest to the Earth in January 2014 at a distance of about 37 million miles. Based on the preliminary numbers, this comet might be one of the brightest in years, almost certainly a naked eye object and visible to everyone from both the northern and southern hemispheres.

To quote the comments from one astronomy forum:
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ESA controllers buy time to solve problems on comet probe Rosetta

This ain’t good. One of the reasons ESA controllers recently put the comet probe Rosetta into hibernation for two and a half years was in order to buy time to solve a serious technical problem.

Mission managers said the hibernation will permit Rosetta to rest its four reaction wheels, two of which have shown signs of degradation. The satellite needs three to function, and one of the two problem wheels will be used only as a spare when the satellite is awakened in January 2014 in preparation for its approach to a comet.