A Story Of Detecting Other Worlds: Direct Imaging
Blocking bright starlight allows us to photograph the faint light of distant exoplanets.
Exoplanets are very difficult to see directly, even with powerful telescopes. Even if the planet is relatively large, the starlight overwhelms the light reflected off the exoplanet. Trying to see an exoplanet orbiting a star is like trying to see a firefly next to a big bright search light from thousands of miles away.
However, with a special tool known as a coronagraph, direct imaging of exoplanets it is possible. A coronagraph is essentially an opaque disc used to block starlight, making it possible to see much fainter objects near the star. As of 2020, about 50 planets—roughly 1% of the total number of confirmed exoplanets—have been discovered through direct imaging using coronagraphs.
The direct images of four giant planets orbiting star HR 8799 shown here were captured by the Keck telescope in Hawaii. The observations provide a special “birds-eye” view of a planetary system. By observing the system over several years, astronomers were able to confirm that four of the bright spots are in fact planets. They were also able to measure how far each planet is from the star; estimate each planet’s size and mass; and predict their full orbits. Telescopes like the James Webb Space Telescope and the upcoming Nancy Grace Roman Space Telescope will use direct imaging to find out more about planets like these and look for additional planets.
Quick Facts: Direct Imaging
Type:
Super-Jupiters
Distance from Earth:
135 light-years
Location in the universe:
Orbiting star HR 8799 (also called V342 Pegasi)
Mass:
Exoplanet HR 8799 b is roughly 6 times the mass of Jupiter; planets c, d, and e are roughly 7 times the mass of Jupiter
Size:
All four planets are about 1.2 times the diameter of Jupiter
Orbital period:
Planet b completes one orbit in about 491 Earth-years; c: about 233 Earth-years; d: about 110 Earth-years; e: about 54 Earth-years
Did you know:
The HR 8799 system is the only directly imaged solar system known to have four super-Jupiter planets.
Credits: Direct Imaging
Infrared coronagraph images of HR 8799 from the Keck Telescope: Jason Wang (Caltech), Christian Marois (NRC Herzberg)
Produced by the Space Telescope Science Institute’s Office of Public Outreach