Webb Scans Vega for Planets

To northern sky watchers, Vega is a familiar sight in the summer sky. It’s one of the brightest stars in the sky and in 2013, astronomers detected a large ring of rocky debris surrounding the planet. The prospect of planets suddenly became a real possibility so astronomers turned the James Webb Space Telescope (JWST) on the star. The hunt achieved 10 times the sensitivity of previous ground based searches but alas no planets were discovered. 

Vega lies in the constellation Lyra and is one of the prominent stars that makes up the Summer Triangle along with Aquila in Altair and Deneb in Cygnus. Vega itself likes 25 light years away from Earth so it is, in astronomical terms, relatively close. It’s a hot blue/white star which has a visible surface temperature of around 9,600 degrees. At this temperature it is hotter than the Sun and in size it is about 2.1 times larger in diameter. 

The track of the ISS near Vega in Lyra. From right to left, the station is passing from sunlight into Earth’s shadow. Its color transitions from white to red. Credit: Bob King

Data captured by JWST has recently been used to study Vega. The space telescope is perhaps the most advanced telescope to be placed into orbit. It was launched in December 2021 as part of a partnership between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA.) It orbits the Sun at the second Lagrange point which is about 1.5 million km away from Earth. As telescopes go it’s not the largest (main mirror is 6.5m across) but by being in space it can out perform many ground-based instruments. 

Among the many instruments on board JWST, NIRCam (Near Infrared Camera) and MIRI (Mid Infrared Camera) have been used to probe the secrets of Vega. Interest was piqued when the Infrared Astronomical Satellite (IRAS) detected an excess of long wavelengths which were attributed to a cold dust ring emitting radiation at 25-100 ?m. Further studies revealed the signal was very similar to the signal from the Kuiper Belt. The discovery led astronomers to the conclusion that it must be the remains of planetary formation. 

MIRI, ( Mid InfraRed Instrument ), flight instrument for the James Webb Space Telescope, JWST, during ambient temperature alignment testing in RAL Space’s clean rooms at STFC’s Rutherford Appleton Laboratory, 8th November 2010.

In a paper written by a team of astronomers led by Charles Beichman from NASA’s Exoplanet Science Institute they describe their attempts to hunt down planets in the ring of debris. They were able to utilise data from NIRCam’s coronographic observations of Vega. Within this data, there were 3 sources identified and analysed using supporting data from MIRI. The sources were assessed to see if astrometric data confirmed an association with Vega. If it were part of the Vega system the data would indicate a mass of these sources between 1 and 3 times mass of Jupiter and a temperature in the region of 250K.

Such an object is likely to have disrupted the smooth disk structure but the MIRI data reveals no such effects. It seems then for now at least, that the debris field around Vega is devoid of evidence of planetary formation. Further studies using the instrumentation on board JWST and other new observatories coming on line may change this view but for now it seems, Vega may just be alone without any planetary system. 

Source : Searching for Planets Orbiting Vega with the James Webb Space Telescope

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