'Oumuamua accelerated by leaving the inner solar system. This could be why.

Astronomers believe that a flip-flop movement could solve the puzzle.

The brief interstellar visitor 'Oumuamua has left many mysteries as a result of his flash flight of the solar system. The changes in its brightness imply that it's a cigar-shaped body being tipped, but we've never seen it close enough to know the true outlines. We do not know exactly what it is made of. We do not know where it comes from, even though we suspect that it was kicked out by another star system by a giant planet.

One of the strangest riddles, however, is that "Oumuamua seemed to touch the gas when it came out of the internal solar system. The body accelerated a little – about a thousandth – more than it should have been if the only lash at its movement came from the gravity of the Sun. The best hypothesis of Marco Micheli (ESA-NEO Coordination Center of ESA and INAF Rome Astronomical Observatory), Karen Meech (Institute of Astronomy of the University of Hawaii) , and their colleagues when they discovered that the anomaly was that of Oumuamua's vapors The surface in the sunlight had kicked the body further. However, no observations had detected such degassing.

Report in a future Letters from the Astrophysical JournalDarryl Seligman (Yale), graduate student, along with his advisors Greg Laughlin (also Yale) and Konstantin Batygin (Caltech) think they've found a solution – and no, it's not an alien spaceship. The team reviewed all the observations made during the Oumuamua "whiplash" visit and concluded that the outgassing may well be to blame.

The researchers looked at what would happen if the incident solar light created a jet of propellant-like vapor at the spot on "Oumuamua that pointed directly to the Sun." When the body collapsed, this place would change location and the created stream would migrate to the surface, as shown in the Seligman video below. (The dark blue arrow that moves – not to be confused with the double arrows of a brighter blue along an axis – marks the jet.)

The small thrust of this jet migration would tilt the body like a pendulum. According to the researchers, this switchover would explain both the acceleration and the periodic diagram of the luminosity of Oumuamua. He also predicts a size for the largest dimension of the body – about 260 meters – which corresponds to estimates based on the brightness of the object, assuming it was covered with ice long exposed to interstellar conditions.

"I think it's a very good document that attempts to responsibly close several interesting data sets," said Meech, who led the main "Oumuamua" observation campaign. "I think they did a very good job."

But Roman Rafikov (University of Cambridge, UK) is more skeptical. None of the authors' curves concerning the luminosity changes of the object reproduce the real light curve, in particular the pointed minima naturally created by an elongated object in rotation. "Just try to spin a cigar along its short axis, and you'll see the periods when you see it [the] small section passes quickly, "he says.

In addition, the degassing should have changed the "Oumuamua spin". Astronomers saw the acceleration of the body divided by four between late October and late November 2017, as the object moved away from the sun. If this change occurred because less sunlight reached the object and thus sublimated less ice, the pendulum swing period of Oumuamua should have doubled, which was not observed.

Laughlin agrees that the period should have doubled as sunlight and outgassing decreased. "However, the information on the exact periods concern only four nights from 24 to 25 October and from 27 to 28 October," he says. Observations starting one month later make show that the period has changed, but we do not know how much.

The team did not try to adapt its model precisely to the real light curve, he adds, because the shape of it is simplified, which allows to vary the proportions. "Oumuamua's body was probably more irregular.

We will never know for sure what happened: 'Oumuamua is now beyond the orbit of Saturn, and she will not come back. We can only prepare ourselves for the next interstellar visitor.

Reference: Seligman, Darryl, Gregory Laughlin and Konstantin Batygin. "On the abnormal acceleration of 1/2017 U1" Oumuamua ". Accepted by Letters from the Astrophysical Journal.

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Read Oumuamua's full article in our latest article by Greg Laughlin.