Telescopes That Changed The Way We Look At Exoplanets

 Have you ever wondered, "What method do astronomers use to detect exoplanets?"

It is hard to detect planets revolving around stars through direct imaging because planets are dim and small and are easily lost in the glare of stars. What we use to study these planets are indirect methods: detecting the dimming of light when a planet passes from in front of the star(transit method) or monitoring the star's spectrum for signs of a planet pulling on it and generating a Doppler shift in the star's light. Other methods include gravitational lensing, radial velocity, and coronagraphs.

Source: scientificamerican.com

The stars' brightness would absorb any light reflected from the planets at visible wavelengths. So we use an infrared wavelength of light as their integral heat burns relatively brightly at longer wavelengths.

Kepler Space Telescope made one of the mind-boggling discoveries that our galaxy has more planets than stars. Here is a series of telescopes that have made amazing discoveries and revealed so many mysteries about exoplanets. 

Spitzer Space Telescope

NASA's Spitzer Space Telescope exploring the universe|Source: nasa.gov

Launched in 2003, Spitzer Space Telescope was an infrared space telescope and the first spacecraft to use the Earth-trailing orbit. It was comprised of two major components:

1. The Cryogenic Telescope Assembly- It is a container for Spitzer's three scientific instruments.

2. The spacecraft- Despite controlling the telescope and supplying power to instruments, it is responsible for handling scientific data and communicating with Earth.

"But what makes this telescope suitable to capture exoplanets?"

Spitzer is so designed that it allows astronomers to view cosmic regions that are inaccessible to optical observatories, such as dusty star nurseries, the centers of galaxies, and newly forming planetary systems. Apart from this, cooler objects like- failed stars, extrasolar planets, giant molecular clouds, and organic molecules that may lead to the origin of life can also be observed through Spitzer.

With the exhaustion of helium (used to cool instruments), Spitzer's prime mission came to an end while warm instruments were operational till 2020.

Kepler Space Telescope

Kepler Space Telescope|Source: jpl.nasa.gov

Kepler Space Telescope was a space observatory dedicated to the search for exoplanets, especially those resembling the Earth. Since its launch in 2009, Astronomers have discovered thousands of extra-solar planets, most of which were between the size of Earth and Neptune. For the initial four years, Kepler observed a small patch of sky to search for shadows(tiny dips in the brightness of individual stars) that the planet makes when it crosses the face of the star. Kepler witnessed thousands of such shadows, called transits.

After losing much of its pointing capability in 2009, a modified K2 mission began, in which Kepler used the pressure of sunlight to stabilize itself. In K2, Kepler looked at the stars in the plane, switching its view to different spots of the sky. According to a NASA press release, after the end of the K2 mission, the total count of the surveyed stars was more than 500,000. Kepler discovered around 2,600 exoplanets, which was the highest of any exoplanet mission.

TESS 

This is a conceptual image of TESS's mission|

Source: nasa.gov

TESS(Transiting Exoplanet Survey Satellite) also observed exoplanets by looking at the transits as Kepler did. But unlike Kepler, it conducted an expansive survey that encompasses almost the entire sky. To do this, TESS orbits the Earth in a rare High Earth Orbit of 12 to 15 days that is angled so that the Telescope's view of the sky is entirely free from interference by our bright planet and moon.

Throughout its two-year primary mission, TESS observed over 200,000 stars and found over 1,900 potential exoplanets. Launched in April 2018, TESS began its extended mission in July 2022 to monitor our stellar neighborhood and identify the planets that reside in it. This time, TESS increased its imaging cadence to search for habitable, Earth-like planets. The search mainly focused on Red Dwarfs because of their lower masses and gravities. 

Hubble Space Telescope 

The Hubble Space Telescope with Earth in its background|Source: nasa.gov

So, here is one of the most famous and revolutionizing telescopes of NASA.

Hubble Space Telescope is a large space-based observatory that was launched in 1990. Investigating everything from Black Holes to planets around stars, Hubble has helped to answer some of the most compelling astronomical questions. It is one of the largest and most versatile that has observed planets inside and outside our solar system and some of the distant galaxies and stars.

Hubble was the first telescope to directly detect an exoplanet's atmosphere and observed the presence of Sodium in the planet's atmosphere through "transit spectroscopy". After the study of the TRAPPIST-1 planetary system in 2018, astronomers observed that at least three planets in Star's habitable zone showed characteristics of a dense atmosphere that might have a fair amount of heavier gases. 

Even after 30 years of its launch, the Hubble Telescope is still operational and is one of the most successful windows to observe exoplanets.

James Webb Telescope

An artist's concept of the Webb Space Telescope|Source: solarsystem.nasa.gov

Recently launched by NASA, it is another great technology attempting to see an alien world.

James Webb Telescope's main aim is to study the atmosphere of exoplanets to look for the elements of life elsewhere in the universe. But how good is Webb at studying exoplanets?

The James Webb Telescope will also use the transit method to study exoplanets and, in collaboration with ground-based telescopes,  will measure the mass of the planets by radial velocity method. In radial velocity, stellar wobble produced by the gravitational tug of planets is measured.

Webb will be able to form direct images of exoplanets near bright stars through coronagraphs. The coronagraph is designed to reduce the dazzling glare of the stars so that planets in their orbits can be seen. Webb has a set of segmented mirrors that enable it to search for water vapor in the atmosphere of exoplanets. Webb will give us new insights about these planets by observing them at wavelengths of light at which they have been never seen before. It is a true technological marvel in search of life.