JWST images sharpen the search for planets around nearby star Altair

Altair is a nearby star about 88 million years old, making it a promising target in the search for young giant planets. JWST observations found no confirmed companions: apparent candidates proved to be background stars. The images can detect planets below Saturn's mass at wide distances, and Altair may also serve as a useful reference star for future observations.

Star system: Altair | Distance from the Sun: 16.7 light years

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JWST images sharpen the search for planets around nearby star Altair

Star system: Altair | Distance from the Sun: 16.7 light years

Two sets of JWST images of Altair found no confirmed planets, but they reached the sensitivity needed to search for low-mass giant planets in wide orbits. Several faint points of light appeared in the first images. Later observations showed that none moved with Altair, and their colors matched those expected for background stars.

The images were taken at two infrared wavelengths using a coronagraph, a device that blocks a star's bright light so nearby, fainter objects are easier to see. After processing, the images could distinguish objects far fainter than Altair: at a separation of about 5.1 astronomical units, the measured contrast was 2 parts per million. At 10.3 astronomical units it was 0.15 parts per million, and beyond about 20 astronomical units it reached a few hundredths of a part per million. An astronomical unit is the average distance between Earth and the Sun.

Models of young planets indicate that this sensitivity corresponds to masses below Jupiter's beyond 5 astronomical units and below Saturn's beyond 10 astronomical units. These are detection limits, not evidence that planets with those masses are present. Altair has no known companions or detected debris disk, and it is not linked to a known group of stars. Its age is estimated at 88 million years, with an uncertainty of 10 million years, and its distance is 5.13 parsecs.

Altair could also help calibrate future imaging observations. Measurements of background stars show that they will remain at least a few arcseconds away from Altair over the next 10 to 20 years. That separation makes Altair a useful reference target for future campaigns, including observations with the Roman Space Telescope's Coronagraph Instrument.

Key findings
Two rounds of JWST imaging found no confirmed planets around Altair.
All candidate points of light were consistent with background stars rather than objects moving with Altair.
The images reached model-based sensitivity to planets below Jupiter's mass beyond 5 astronomical units and below Saturn's mass beyond 10 astronomical units.
Altair is about 88 million years old and 5.13 parsecs from the Sun.
Background stars are expected to remain a few arcseconds or more from Altair for 10 to 20 years, supporting its use as a future reference target.

Scientific study

Searching for Planets around Altair with JWST/NIRcam