TESS Spots Comet Orbiting Bright Star Beta Pictoris

Comets around Beta Pictoris have fascinated astronomers so much that artists' impressions have been created, and now we have found the dimming as one passed across the star's face. ESO/L. Calçada/N. Risinger

The Transiting Exoplanet Survey Satellite (TESS) has found a comet orbiting Beta Pictoris, a star that has provided us with our first, and some of our best, insights into the process by which planetary systems form. Comets were first detected around Beta Pictoris in 1984, beating the first discovery of a planet around another star, but TESS has allowed us to learn about an individual object in a way that previous instruments could not.

In 1984 a study of infrared radiation from Beta Pictoris demonstrated the source was a disk similar in size to the Solar System, providing the first sign the Sun's family of planets and comets was not unique.

Three years later absorption features in the light from Beta Pictoris were attributed to the tails of comets. Even 30 years later, fewer than a dozen other stars have produced a similar cometary signal. Now Professor Konstanze Zwintz of the University of Innsbruck has announced in a paper submitted to Astronomy and Astrophysics (preprint on arXiv) the detection of a specific Beta Pictoris comet, observing the fading and rebrightening of the star's light as a comet passed in front. The advantage of this method is that we can learn about specific comets, rather than just knowing they exist.

The pattern of dimming exactly matches the one predicted in a 1999 paper proposing to astronomers what they needed to look out for to distinguish dimming caused by comets from the contribution of other sources.

So far Zwintz has not been able to determine this comet's orbit with certainty, but the paper proposes it is probably on a highly eccentric orbit, no further out than three times the distance between the Earth and the Sun, and probably less. The tail appears quite small, with most dust concentrated near the nucleus.

There is reason to think Beta Pictoris has an abundance of comets. Besides the original detection of gases absorbing particular wavelengths of light, the distinctive spectral signal of carbon monoxide has been explained as the product of collisions between comets, something very unlikely unless there are a lot of them.

Beta Pictoris is 63 light-years away making it one of the closest stars to us, particularly if you exclude red dwarfs. At 23 million years old, its companions are likely still forming. The one planet we know of is so big – 13 times the mass of Jupiter – and so distant from its star we are able to image it directly without it being lost in the glare.

Learning about other cometary systems may help us settle the vexed question of whether comets are responsible for the unexplained dimming of Boyajian's star, whose strange behavior was also attributed to an alien megastructure.


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