Hubble uses microlensing to find Uranus-sized planet around distant star

NASA’s Hubble Space Telescope and the W.M. Keck Observatory in Hawaii have independently confirmed the discovery of a giant exoplanet orbiting far from its central star. The planet was discovered through a technique called gravitational microlensing.

This findings were published in two papers in the The Astrophysical Journal.

The discovery is significant as most exoplanets found so far orbit very close to their host stars. Techniques for finding the distant worlds favour finding planets in these shorter orbits, which is why scientists are also the microlensing technique, which can find more distant and colder planets in long-period orbits.

Microlensing, explained in the video above, occurs when a foreground star amplifies the light of a background star that momentarily aligns with it.  If the foreground star has planets, then the planets may also amplify the light of the background star, but for a much shorter period of time than their host star. The exact timing and amount of light amplification can reveal clues to the nature of the foreground star and its accompanying planets.

The system where the giant was discovered has been cataloged as OGLE-2005-BLG-169. It was discovered in 2005. Now the Hubble and the Keck Observatory teams have found that the system consists of a Uranus-sized planet orbiting about 600 million kilometres from its parent star, slightly less than the distance between Jupiter and the Sun. The host star, however, is about 70% as massive as our Sun.

“These chance alignments are rare, occurring only about once every 1 million years for a given planet, so it was thought that a very long wait would be required before the planetary microlensing signal could be confirmed,” said David Bennett, the lead of the team that analysed the Hubble data.

“Fortunately, the planetary signal predicts how fast the apparent positions of the background star and planetary host star will separate, and our observations have confirmed this prediction. The Hubble and Keck Observatory data, therefore, provide the first confirmation of a planetary microlensing signal.”

Microlensing is such a powerful tool that it can uncover planets whose host stars cannot be seen by most telescopes.

“It is remarkable that we can detect planets orbiting unseen stars, but we’d really like to know something about the stars that these planets orbit,” explained Virginie Batista, leader of the Keck Observatory analysis.

“The Keck and Hubble telescopes allow us to detect these faint planetary host stars and determine their properties.”