First Observation of an Interstellar Visitor

[Tank]

For other ignoramuses like me, "sublimation" is when a solid goes to the gaseous phase without passing through the liquid phase, like ice cubes shrinking in the freezer. 

I propose making a cigar named Oumuamua and smoking it in honor of Oumuamua.

Another example which is often given, but incorrectly, is iodine crystals. When heated, Iodine does in fact melt at 114°. One can boil the liquid iodine in a test tube to dry it, as I did many times when I needed anhydrous iodine. The boiling point is around 185°, when it refluxes on the inside walls of the test tube.

I love a 'geek mode' moment 

[hermes2015]

For other ignoramuses like me, "sublimation" is when a solid goes to the gaseous phase without passing through the liquid phase, like ice cubes shrinking in the freezer. 

I propose making a cigar named Oumuamua and smoking it in honor of Oumuamua.

Another example which is often given, but incorrectly, is iodine crystals. When heated, Iodine does in fact melt at 114°. One can boil the liquid iodine in a test tube to dry it, as I did many times when I needed anhydrous iodine. The boiling point is around 185°, when it refluxes on the inside walls of the test tube.

I love a 'geek mode' moment 

Thank you (I think). Not sure whether that is good or bad.

[xSilverPhinx]

For other ignoramuses like me, "sublimation" is when a solid goes to the gaseous phase without passing through the liquid phase, like ice cubes shrinking in the freezer. 

I propose making a cigar named Oumuamua and smoking it in honor of Oumuamua.

Another example which is often given, but incorrectly, is iodine crystals. When heated, Iodine does in fact melt at 114°. One can boil the liquid iodine in a test tube to dry it, as I did many times when I needed anhydrous iodine. The boiling point is around 185°, when it refluxes on the inside walls of the test tube.

I love a 'geek mode' moment 

Thank you (I think). Not sure whether that is good or bad.

It's good, no matter what others might say.

[xSilverPhinx]

I propose making a cigar named Oumuamua and smoking it in honor of Oumuamua.

To Oomua...Ohmua...to *inaudible muffled sound*. 

[Randy]

 

[Recusant]

A new hypothesis for the origin of 'Oumuamua.  Instead of hydrogen, the papers described below suggest that it was mostly composed of nitrogen.

"Interstellar Object 'Oumuamua Is Likely a Piece of a Pluto-Like Planet" | American Geophysical Union

Illustration of a plausible history for 'Oumuamua shows an origin in its parent system around 0.4 billion years ago; erosion by cosmic rays during its journey to the solar system; and passage through the solar system, including its closest approach to the Sun on 9 September 2017 and its discovery in October 2017. At each point along its history, this illustration shows the predicted size of 'Oumuamua, and the ratio between its longest and shortest dimensions.
Graphic credit: S. Selkirk/ASU,

The first known interstellar object to pass through our solar system is likely a piece of a Pluto-like planet from another solar system, according to a new study published as a pair of papers today in the Journal of Geophysical Research: Planets, AGU's journal for research on the formation and evolution of the planets, moons and objects of our solar system and beyond.

The results may help scientists learn about the stuff exoplanets are made of and the evolution of solar systems beyond our own.

"This research is exciting in that we've probably resolved the mystery of what 'Oumuamua is and we can reasonably identify it as a chunk of an 'exo-Pluto,' a Pluto-like planet in another solar system," said Steven Desch, an astrophysicist at Arizona State University and an author of the new study. "Until now, we've had no way to know if other solar systems have Pluto-like planets, but now we have seen a chunk of one pass by Earth."

Discovered in 2017 via the Pan-STARRS astronomical observatory in Hawaii, 1I/2017 U1 'Oumuamua, meaning 'scout' or 'messenger' in Hawaiian, hurtled past at 87.3 kilometers per second (196,000 miles per hour). The weirdly flat object was like a comet, but with features that were just odd enough to defy classification.

'Oumuamua's characteristics suggest it is likely made of solid nitrogen, like the surface of Pluto, according to the authors.

"It was likely knocked off the surface by an impact about half a billion years ago and thrown out of its parent system," said Alan Jackson, an astronomer and planetary scientist at Arizona State University and coauthor of the new study. Jackson will present the research on Wednesday, 17 March at the 52nd Lunar and Planetary Sciences Conference.

'Oumuamua likely wasn't flat when it entered our solar system, but melted away to a sliver, losing more than 95% of its mass, during its close encounter with the Sun, according to Jackson.

[Continues . . .]

There are links to the papers available at the AGU press release page above.

[Randy]

I didn't realize that people were still studying that thing. it's got to be pretty far out there by now. it must be from pictures taken on it's approach.

[Davin]

I didn't read this specific article, only the provided snippet, I'll read the rest later.

It had been detected that it picked up speed which is common for comets that get close to a star from an out-gassing process. But this one didn't look like the same kind of ice that would produce that kind of thing. Which is why they think it's likely nitrogen because when they plug nitrogen into the equations it matches all observed behavior. So unfortunately it's not and alien ship... at least not proven.

Now we'll have to see if that guy who wrote a book about how it's definitely aliens will handle this, correct himself or start speaking on the alien convention circuit.

[Recusant]

A refinement of the outgassing explanation for the observed acceleration. Those damned scientists are determined to stomp on our fantasies of interstellar voyagers. 

"Sorry, E.T. fans: Interstellar visitor 'Oumuamua isn't an alien spacecraft. It's just passing gas." | Space.com

Since its surprise arrival in the solar system in 2017, the interstellar object 'Oumuamua has puzzled scientists. A duo of American astronomers now think they have solved one of the space rock's lingering mysteries.

First thought to be an asteroid, later recast as a likely comet, and by some even considered a possible alien spaceship, the 650-foot-long (200 meters) 'Oumuamua zoomed through the central solar system in late 2017. During its brief visit, the rock approached Earth within 15 million miles (24 million kilometers), about 62 Earth-moon distances, and disappeared a few weeks after its discovery.

Observations made within this short period of time soon proved that 'Oumuamua was on what astronomers call a "hyperbolic" orbit, a boomerang-shaped trajectory that indicated the rock is not native to our solar system but was only passing through the sun's neighborhood and would never be seen again.

[. . .]

Many scientists have tried to explain the mechanism behind 'Oumuamua's acceleration, but all of the proposed ideas have had significant gaps. In a new study, Jennifer Bergner, an assistant professor of chemistry at the University of California, Berkeley and Darryl Seligman, a U.S. National Science Foundation postdoctoral fellow at Cornell University, propose a new theory, which they think might finally put the issue to rest.

"I have been trying to explain the outgassing for several years now," Seligman told Space.com. "First, I thought that perhaps there just wasn't too much dust in the outgassing [to form the coma]. Later, we thought that perhaps it was made of some more volatile material than what we see in usual comets, such as hydrogen, nitrogen or carbon monoxide. But there were theoretical issues with each of these explanations."

Hydrogen, for example, would require extremely cold temperatures to freeze into objects the size of 'Oumuamua, and scientists don't expect such temperatures inside the dense molecular clouds where these objects form, Seligman said. Nitrogen is not ubiquitous enough in the Milky Way to account for the expected number of such bodies in the galaxy, he added.

Seligman and Bergner now propose that there might be nothing extraordinary about 'Oumuamua's chemistry. Instead, the object was subject to processes outside the solar system that astronomers don't know about from our observations of domestic comets.

"A comet traveling through the interstellar medium basically is getting cooked by cosmic radiation, forming hydrogen as a result," Bergner said in a statement(opens in new tab). "Our thought was: If this was happening, could you actually trap it in the body, so that when it entered the solar system and it was warmed up, it would outgas that hydrogen?"

Continues . . .

The paper is behind a paywall.

Abstract:

In 2017, 1I/'Oumuamua was identified as the first known interstellar object in the Solar System. Although typical cometary activity tracers were not detected, 'Oumuamua showed a notable non-gravitational acceleration. So far, there has been no explanation that can reconcile these constraints.

Owing to energetic considerations, outgassing of hyper-volatile molecules is favoured over heavier volatiles such as H2O and CO2. However, there are theoretical and/or observational inconsistencies with existing models invoking the sublimation of pure H2, N2 and CO. Non-outgassing explanations require fine-tuned formation mechanisms and/or unrealistic progenitor production rates.

Here we report that the acceleration of 'Oumuamua is due to the release of entrapped molecular hydrogen that formed through energetic processing of an H2O-rich icy body. In this model, 'Oumuamua began as an icy planetesimal that was irradiated at low temperatures by cosmic rays during its interstellar journey, and experienced warming during its passage through the Solar System.

This explanation is supported by a large body of experimental work showing that H2 is efficiently and generically produced from H2O ice processing, and that the entrapped H2 is released over a broad range of temperatures during annealing of the amorphous water matrix. We show that this mechanism can explain many of 'Oumuamua's peculiar properties without fine-tuning. This provides further support that 'Oumuamua originated as a planetesimal relic broadly similar to Solar System comets.

[Tank]

Bloody kill joys 

[Asmodean]

The Asmo's own people, those.

Second Law of Asmodynamics clearly states that if a parade can be rained on, then you should bring a umbrella.

[Recusant]

A third observation of an interstellar object passing through our solar system.

"It's Official: NASA Confirms New Interstellar Object Is Zooming Through Solar System" | Science Alert

Astronomers on Wednesday confirmed the discovery of an interstellar object racing through our Solar System – only the third ever spotted, though scientists suspect many more may slip past unnoticed.

The visitor from the stars, designated 3I/Atlas by the International Astronomical Union's Minor Planet Center, is likely the largest yet detected. It has been classified as a comet.

"The fact that we see some fuzziness suggests that it is mostly ice rather than mostly rock," Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, told AFP.

Originally known as A11pl3Z before it was confirmed to be of interstellar origin, the object poses no threat to Earth, said Richard Moissl, head of planetary defense at the European Space Agency.

"It will fly deep through the Solar System, passing just inside the orbit of Mars," but will not hit our neighbouring planet, he said.

[Continues . . .]

"NASA Discovers Interstellar Comet Moving Through Solar System" | NASA

On July 1, the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile, first reported observations of a comet that originated from interstellar space. Arriving from the direction of the constellation Sagittarius, the interstellar comet has been officially named 3I/ATLAS. It is currently located about 420 million miles (670 million kilometers) away.

Since that first report, observations from before the discovery have been gathered from the archives of three different ATLAS telescopes around the world and the Zwicky Transient Facility at the Palomar Observatory in San Diego County, California. These "pre-discovery" observations extend back to June 14. Numerous telescopes have reported additional observations since the object was first reported.

The comet poses no threat to Earth and will remain at a distance of at least 1.6 astronomical units (about 150 million miles or 240 million km). It is currently about 4.5 au (about 416 million miles or 670 million km) from the Sun. 3I/ATLAS will reach its closest approach to the Sun around Oct. 30, at a distance of 1.4 au (about 130 million miles or 210 million km) — just inside the orbit of Mars.

The interstellar comet's size and physical properties are being investigated by astronomers around the world. 3I/ATLAS should remain visible to ground-based telescopes through September, after which it will pass too close to the Sun to observe. It is expected to reappear on the other side of the Sun by early December, allowing for renewed observations.

[Tank]

We may well see more of these now the Vera Rubens telescope is online.

[Dark Lightning]

All kinds of things whizzing through our little solar system. Those kinds of trajectories will give us little, if any, time to react if it's coming directly for our planet. Good thing space is so...spacious.

[Recusant]

I think it's a bit presumptuous to call this latest visitor "bizarre" given that it's only the third one we've spotted, but it's certainly intriguing.

"4 Powerful Telescopes Agree: Interstellar Comet 3I/ATLAS Really Is Bizarre" | Science Alert

We already knew that interstellar comet 3I/ATLAS was different from the other two interstellar objects known to have traversed the Solar System, but a slew of new observations suggest it may be even weirder than the weirder that it was.

NASA and ESA instruments Hubble, SPHEREx, JWST, and TESS have all captured the object as it makes its way towards the Sun. The results show that not only was 3I/ATLAS actively outgassing long before we spotted it, but its atmosphere (or coma) has a higher proportion of carbon dioxide than scientists usually see in comets, interstellar or otherwise.

This could tell us something about the environment in which 3I/ATLAS formed, the space conditions through which it has traveled, or even the internal composition of the comet.The comet first came to our attention on 1 July 2025, and astronomers have been avidly goggling at it ever since – not least because they have a very limited window in which to do so. Its closest approach to the Sun, or perihelion, will take place on October 29; but, because it's on the other side of the Sun from Earth, it will be hidden behind the star's blazing glow by this time.

This means that the best time for observing the comet before perihelion is rapidly slipping by, so scientists are making the best of it, turning some of our most powerful instruments to the task – or, in the case of TESS, scouring pre-discovery data for glimpses of the object.

It's for this reason that we now know the first known glimpse of 3I/ATLAS took place back in May, nearly two full months before the official discovery. The comet was moving a lot faster than the targets TESS is designed to study, so researchers had to use some image-stacking techniques to reveal it.

This is where it gets interesting. The TESS data suggest that the comet was already active at that time, at a distance of around 6 astronomical units (AU) from the Sun – out past the orbit of Jupiter. That's a much greater distance than expected: most comets begin showing activity no closer than 5 AU from the Sun.

When we call a comet active, it means that it has warmed up enough for the ices on and just under its surface to sublime – transition directly from a frozen to a gaseous state. This produces a coma and, eventually, if the comet comes close enough to the Sun to be affected by radiation pressure, cometary tails.

In their preprint paper, the researchers who made the TESS discovery posit that the comet's early awakening may have had something to do with its composition. Some ices sublime more readily than others – and carbon dioxide is one of those ices.

[Continues . . .]

The preprint paper is open access:

"Precovery Observations of 3I/ATLAS from TESS Suggests Possible Distant Activity" | arXiv

Abstract:

3I/ATLAS is the third macroscopic interstellar object detected traversing the Solar System. Since its initial discovery on UT 01 July 2025, hundreds of hours on a range of observational facilities have been dedicated to measure the physical properties of this object.

These observations have provided astrometry to refine the orbital solution, photometry to measure the color, a rotation period and secular light curve, and spectroscopy to characterize the composition of the coma. Here, we report precovery photometry of 3I/ATLAS as observed with NASA's Transiting Exoplanet Survey Satellite (TESS). 3I/ATLAS was observed nearly continuously by TESS from UT 07 May 2025 to 02 June 2025.

We use the shift-stack method to create deep stack images to recover the object. These composite images reveal that 3I/ATLAS has an average TESS magnitude of T_mag = 20.83 ± 0.05,19.28 ± 0.05 and an absolute visual magnitude of Hv = 13.72±0.35;12.52±0.35, the latter being consistent with magnitudes reported in July 2025.

When coupled with recent HST [Hubble Space Telescope] images deriving a nucleus size of R<2.8 km (H>15.4), our measurements suggest that 3I/ATLAS may have been active out at ∼ 6 au. Additionally, we extract a  day light curve and find no statistically significant evidence of a nucleus rotation period.

Nevertheless, the data presented here are some of the earliest precovery images of 3I/ATLAS and may be used in conjunction with future observations to constrain the properties of our third interstellar interloper.