Saturn In Near-infrared

Saturn in near-infrared

HOW DO ASTRONOMERS DETECT EXOPLANETS AND DETERMINE IF THEY COULD SUPPORT LIFE??

Blog#335

Wednesday, September 27th, 2023

Welcome back,

On March 21, NASA announced the confirmation of the 5,000th planet outside our Solar System. From scorching-hot gas giants nestled near their parent star to rocky worlds that may host water on their surface, there’s a variety for scientists to study.

But finding these strange new worlds is a science in itself.

HOW DO ASTRONOMERS DETECT EXOPLANETS AND DETERMINE IF THEY COULD SUPPORT LIFE??

We’ve only been able to definitively detect planets of any kind for a few decades, and even at that, there are challenges in detecting such a small object at that distance in even the most powerful telescopes.

Inverse spoke with Marie-Eve Naud, an exoplanet researcher and outreach coordinator for the University of Montreal’s Institute for Research on Exoplanets, to tell us more about how astronomers find these worlds and the considerations for each method.

While there are numerous methods, the ones cited below are the most common.

THE TRANSIT METHOD

Astronomers have discovered most exoplanets using the transit method, notably with NASA's Kepler telescope launched in 2009. This method observes planets as they pass in front of their stars, causing a slight dimming of starlight, which photometers can detect. This approach works best in space due to minimal atmospheric interference, favored by missions like ESA's Cheops and NASA's TESS.

To confirm exoplanets, multiple transits are necessary to rule out sunspots or dust as causes of light fluctuations. Typically, two or three transits are required to gather substantial data.

Once a planet is detected, astronomers can estimate its radius, while mass is often determined through the radial velocity method. The combination of mass and radius helps classify a planet as rocky or gaseous, impacting its potential habitability.

Factors like proximity to an active star and radiation levels also affect habitability assessments, as seen with TRAPPIST-1's uncertain habitability despite hosting seven Earth-sized planets in its habitable zone.

RADIAL-VELOCITY METHOD

The radial velocity method is commonly used to discover planets, particularly with instruments like HARPS at the European Southern Observatory’s La Silla 3.6m telescope in Chile.

Planets and stars both orbit around their center of mass. A star with a planet exhibits a slight motion. Multiple planets can lead to complex motions.

This method involves analyzing the star's spectrum. When the star approaches, its light shifts towards red due to compression. When it moves away, the light shifts towards blue.

The planet's motion slightly affects the star's spectrum, creating a "barcode" of the star.

The first detection of a planet around a Sun-like star using this method was in 1995 when Didier Queloz and Michel Mayor found 51 Pegasi b. Prior to that, in 1992, planets were detected around pulsar PSR B1257+12, using changes in the pulsar's radio signal. This showcases the diverse scientific approaches to discovering distant worlds.