ARTICLE • OUTER SPACE

To Infinity and Beyond: Exoplanets

by Liv Licardo

51 Pegasi B, the first planet outside of the Solar System to be discovered.

When you were in elementary school, you probably had to learn about the Solar System in your science class and memorize the names of the planets with that one mnemonic. Maybe you grew up watching E.T. or Avatar, and truly believe that there are aliens out there on some undiscovered planet. Or maybe you’re just really into Marvel and believe that Knowhere really exists. Whatever it is, you probably already believe that there are planets outside our solar system that house some intergalactic creatures — and you’re at least half-right.

Beyond our Solar System

Planets do exist outside our main eight planets, called exoplanets. The first exoplanet was confirmed in January 1995 when Didier Queloz, a grad student at the University of Geneva, spotted a fast-moving gas giant orbiting a star.

The planet, now known as 51 Pegasi B or “Dimidium”, was estimated to be half the size of Jupiter. Queloz and Michel Mayor, his adviser, had been hunting for extrasolar planets through wobbles.

This wobble method was used to measure a star’s radial velocity by alternating in squeezing and stretching the star’s wavelength as it moved away and towards us. Their discovery kicked off a planet hunt, with hundreds of new exoplanet discoveries within the next decade, all of them exhibiting nearly similar characteristics — big, star-hugging planets tightly orbiting their parent stars.

If one observed a star’s light frequency to be changing, it can be inferred that there is an exoplanet tugging on it — due to gravity — and causing it to wobble. The change in the light frequency is called a Doppler Shift. Illustration by EarthSky.

Modern Planet Hunting

In 2009, the era of modern “planet-hunting” began when NASA launched their Kepler Space Telescope. The telescope faced a small blanket of sky, and sat there for the next four years, observing the 150,000 stars it could see. Kepler was waiting to catch tiny dips of light, where planets crossed in front of their parent stars. From the data it collected, more two thousand exoplanets were sifted out and confirmed.

NASA’s Kepler Space Telescope, whose goal was to explore the Milky Way and find other planets in it. Photo by NASA.

While we’re still harvesting data from Kepler’s four years of observation, its first mission was shut down in 2013 after two reaction wheels failed to function. Luckily, a little of the instrument was salvaged when the Kepler team created a quick fix by using the pressure of sunlight to stabilize one of the axis of the tele-scope. After renaming it “K2”, the telescope went back to work discovering planets, but at shorter time intervals than its predecessor.

The Search for Earth’s Twin

While we’ve already had a number of discovered exoplanets out there — 3705 confirmed exoplanets, to be exact — the ultimate “wow” moment that astronomers are searching for is evidence of an exoplanet that is habitable to life. Aside from the possibility of actual aliens existing out there, there’s also the promising idea of a new world that humans could visit.

But the search for a habitable planet is harder than it seems. While scientists’ understanding of what makes a habitable planet is continuously evolving, the list of non-negotiables already creates a daunting criteria for Earth’s twin.

The view of Earth, one of the basis of life for scientists, from outer space. Photo by NASA on the Conde Nast Traveller.

The need for water comes first, narrowing the search to planets within the right temperature and distance from the sun that could possibly provide them water. The type and size of the star or planet also comes into play, as gas giants would need to be at a farther distance from the sun than cool dwarf planets. The age of the planet would also be an important factor, taking into account how bright stars tend to burn out quickly and how it took four billion years for Earth to completely form and create multicellular creatures.

Overall, the picture of the planet that scientists are looking for is likely a long-lived dwarf star planet that would be about the same size and composition of Earth, tucked in a habitable zone. If we’re going to talk about what we know, a terrestrial, rocky planet would add to that criteria. However, with most planets being a gas or ice giant, we’re down to a small handful of dwarf planets that have yet to show any signs of life.

The Right Place to Live

In 20 years of space exploration, we’ve confirmed more than three thousand exoplanets, with more than two thousand of those discovered by Kepler. Throw in the unconfirmed planets, and it adds up to more than six thousand candidates. While we’ve yet to see glimpses of the of life on another planet, the very existence of other planets is enough to tell us that there’s a whole new world waiting for us out there — one that is yet to be discovered.

A model of a rover, which is a device designed for space exploration that can help us find signs of life on other planets. Photo by NASA.

REFERENCES

  • How do we find habitable planets? by Pat Brennan via NASA.
  • Exoplanets: Worlds beyond our solar system by Elizabeth Howell via Space.com.
  • How the first exoplanets were discovered by John Wenz via Astronomy.com.
  • 20 Intriguing Exoplanets by Whitney Clavin via NASA.

#ARCHIVES: This article was previously published in Hiraya Zine Volume 1, Issue 1 [Pilot] last July 2020. Download the zine for free here.

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Hiraya Zine

Hiraya Zine

Flagship project of SciCreate, bridging the gap between researchers and the youth through the use of art, writing, and the humanities in quarterly zine issues.