Are there other planetary systems like ours?

Almost certainly yes. Nearly every star in the night sky is likely to have planets around it. Astronomers don’t yet know for certain if any of those planetary systems are like ours. But they hope to find out soon.

How easy is it to find planets around other stars?

It depends on the method used. Seeing a planet orbiting even the star nearest to Earth by direct imaging (detecting the light reflected off of it or the infrared radiation emitted by it) isn’t easy. It’s like trying to see a firefly next to a searchlight. A solar-type star (that is, a star that’s similar to the Sun) is a billion times brighter than a planet like Earth, making planets hard to spot. But telescopes and the methods of processing the astronomical data they collect have become so sophisticated that they can do this and more.

Astronomers can detect planets in other ways besides direct imaging. For example, they spot some by the wobbles the planets produce in the stars they orbit. Others are found because of a slight drop in light from stars when planets pass in front of them.

An artist’s concept of what exoplanet Kepler 452b, the first near-Earth-size planet found in the habitable zone of a star similar to our Sun, might look like. (The habitable zone = a region around a star where temperatures are right for water to pool on the surface.) The planet is about 60% larger than the Earth and orbits its star every 385 days. Credit

So how many planets have we found so far?

Astronomers discovered the first planets orbiting other stars in the mid-1990s—not that long ago. Since then they have added thousands to their database. One big surprise has been that exoplanets, as they are called, come in so many compositions, sizes, and orbits. Planets consist of rock, liquids, gas, and combinations of all three. Some are smaller than Earth while others are larger than any of the planets in the solar system. Some orbit their stars in just a few hours, while others take many thousands of our years to make a single orbit. (The longest orbit discovered so far takes 900,000 Earth years to complete!)

When a planet passes in front of a star, it dims the star’s light by a slight but measurable amount—one method astronomers use to detect exoplanets. Credit

Are there plans to search for more exoplanets?

Yes, ground- and space-based telescopes now being built and those planned to be in use in the coming decade will find more exoplanets and researchers will learn more about the characteristics of planetary systems around other stars. For instance, the James Webb Space Telescope, due to launch in 2021, will be able to probe the thick, massive clouds of dust, called protoplanetary disks, where stars and their planetary systems form. That will likely help scientists acquire new knowledge about the structure and composition of large exoplanets orbiting nearby stars.

The Wide Field Infrared Survey Telescope, set to launch in the mid-2020s, will look for tiny deflections of light from background stars to infer the presence of exoplanets (another detection method). It will be especially effective in determining whether Earth-size exoplanets are common in orbits like ours.

On the ground, a new generation of telescopes using giant segmented mirrors could search for signs of life on exoplanets.

So is it all about telescopes?

Large telescopes are the most visible tools in astronomy, but smaller instruments and research programs are essential to optimize the advance of knowledge. For example, research programs focused on the continued study of the planets in the solar system will provide information about how exoplanets form around other stars.

An illustration of NASA’s Wide Field Infrared Survey Telescope (WFIRST). When it launches in the mid-2020s, this telescope’s sophisticated technology will block out the glare from distant stars, revealing the planets in orbit around them. Credit

Is there life on any of these exoplanets?

We’re on the verge of determining that. Astronomers are finding increasing numbers of rocky planets that are the right distance from their stars for liquid water to exist on their surfaces. While other factors will determine whether such exoplanets harbor life, the presence of liquid water is an essential prerequisite to all known life-forms.

Researchers are also increasingly able to determine the chemical composition of atmospheres around planets. Other stars are too far away to send spacecraft to look for life. But the detection of chemical gases, such as oxygen and methane, might suggest the presence of life-forms as we understand them on Earth. Detection of the absorption and reflection of light—or spectroscopic signatures— associated with vegetation would be an even more compelling signal.

The Earth rising above the Moon, as seen by the Apollo 8 astronauts on December 24, 1968, while they orbited the Moon. Bill Anders, the lunar module pilot who took the photo, reflected on this unique perspective of Earth: “Once-distant places appeared inseparably close. Borders that once rendered division vanished. All of humanity appeared joined together on this glorious-but-fragile sphere.” Credit

Remind me: Why does learning about space matter?

The exploration of space remains one of humanity’s greatest adventures. The discovery of another planet that bears signs of life would transform our understanding of biology and of ourselves. It would be among the most important discoveries ever made.

Astronomy stirs the imagination. It inspires us to learn more about the world and about the universe in which we live. A single astronomical image—like the photograph of Earth rising above the Moon taken from Apollo 8 or the image of the stellar nursery in the Eagle Nebula from the Hubble Space Telescope—can have a profound and long-lasting impact. Astronomical themes also appear in many popular movies, and many terms from the field—such as quasar and black hole—have entered our common vocabulary.

Astronomy is also an inherently international endeavor. Modern telescopes are so large and complicated that they require collaboration among nations. And all people share the night sky, no matter what else divides us.

Take a Deep Dive

Gravitating toward more info about what’s beyond our solar system? Land on these resources for more information: An Astrobiology Strategy for the Search for Life in the Universe and Exoplanet Science Strategy.

Know it all? Prove it.