How astronomers detect new exoplanets
Astronomers began to detect exoplanets relatively recently and today the number of confirmed ones is just over 5,000 while there are more than 8,500 that still have to be confirmed with additional observations and research.
Most of them are detected using the method of transit photometry, and only about a percent can be seen directly. The reason for this is that the emission of light from exoplanets is weaker than that of the star next to them.
During direct observation of stellar systems, their image is collected in the focal plane of the telescope. Due to the diffraction limit, the image of celestial bodies turns out to be blurred, which inevitably leads to errors, both false positive (they saw a planet where there isn’t one) and false negative (they did not see the planet, although it is there). Due to the rarity of exoplanets, type 2 errors are much more critical, so astronomers try to avoid them.
The Kepler Space Telescope discovered around 5000 exoplanet candidates
The Kepler Space Telescope was launched in 2009 and its main task was to search for exoplanets using the transit photometry method. During the years of operation, the device discovered around 5000 exoplanet candidates, of which nearly 2700 were confirmed.
In 2013, due to a gyroscope failure, Kepler’s work was terminated, but then the engineers managed to restore the orientation of the telescope using solar radiation, and in 2014 a new K2 mission began. On October 30, 2018, NASA made the decision to officially shut down the observatory due to frequent breakdowns and running out of fuel.
The huge and public archive of data accumulated by the telescope has allowed many projects to search for new exoplanets, including within the framework of civilian science. Their results show that it is still possible both to detect previously unknown objects on a planetary scale, and to collect data on the distribution of planets by size and mass from stars of the same type.
The TESS Telescope continued Kepler’s work
The TESS (Transiting Exoplanet Survey Satellite) went into space in the spring of 2018, and scientific observations began a few months after launch. The telescope searches for exoplanets near bright stars close to the Sun, tracking periodic dips in their brightness during the passage of the planet across the disk of the star.
At the same time, unlike the Kepler telescope, the search covers 85 percent of the entire sky, divided into 26 sectors. Of primary interest to TESS are small planets, especially rocky ones, that may be in the habitable zone of their stars.
The telescope is most sensitive to exoplanets with an orbital period of fewer than 13 days but is able to find objects with a period of more than 100 days.
In mid-2020, the telescope completed its main science program, having scanned about 75 percent of the celestial sphere, after which it embarked on an extended science program that includes the northern and southern hemispheres of the sky, the ecliptic region, and areas previously observed by the Kepler telescope. By 2021, the number of exoplanet candidates found by TESS (this requires observing two planetary transit events across the disk of a star) has exceeded 2,400.
On January 20, 2022, the leaders of the TESS science program from the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology summed up the current interim results of the work. The number of found candidates for exoplanets amounted to 5210 pieces, of which around 200 have already been confirmed by observational data from ground-based telescopes.
Overall, the primary TESS mission ended in 2020 and has since been extended indefinitely. It will continue to operate and research the universe until it runs out of fuel like Kepler.
We have 5000 confirmed exoplanets – what now?
In just 30 years, astronomers have confirmed the existence of 5,000 exoplanets with thousands more waiting in the candidates’ catalog. Each year, we learn countless new things about the universe and we find more and more Earth-like planets.
With the launch of the new James Webb Space Telescope, which is set to begin scientific observations in the summer, we look forward to the countless discoveries that will be made in the upcoming decade.
The advanced new observatory will rewrite the history of exoplanet research as it will provide an answer to the most important question about these 5000 confirmed exoplanets – are any of them truly habitable?