NASA: 7 Earth-sized planets discovered, 'second Earth' not a 'matter of if but when'

Seven Earth-sized planets have been discovered orbiting a nearby star, three of which appear to be warm enough to sustain life, according to astronomers from NASA and the European Southern Observatory.

The newly discovered exoplanets are 40 light-years away and may contain liquid water.

A Belgian-led team made the discovery using both space- and ground-based telescopes, spotting the planets as they passed in front of the red dwarf star known as TRAPPIST-1.

"This discovery gives us a hint that finding a second earth is not a matter of if but when," said Thomas Zurbuchen, Assoc. Admin., Science Mission Director at NASA.

See what life might look like on these planets:

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Images from NASA on the largest batch of Earth-size, habitable zone planets
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Images from NASA on the largest batch of Earth-size, habitable zone planets
This chart shows, on the top row, artist concepts of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii and masses as compared to those of Earth. On the bottom row, the same numbers are displayed for the bodies of our inner solar system: Mercury, Venus, Earth and Mars. The TRAPPIST-1 planets orbit their star extremely closely, with periods ranging from 1.5 to only about 20 days. This is much shorter than the period of Mercury, which orbits our sun in about 88 days.
This poster imagines what a trip to TRAPPIST-1e might be like.
This artist's concept allows us to imagine what it would be like to stand on the surface of the exoplanet TRAPPIST-1f, located in the TRAPPIST-1 system in the constellation Aquarius.
This data plot shows infrared observations by NASAs Spitzer Space Telescope of a system of seven planets orbiting TRAPPIST-1, an ultracool dwarf star. Over 21 days, Spitzer measured the drop in light as each planet passed in front of the star. Spitzer was able to identify a total of seven rocky worlds, including three in the habitable zone where liquid water might be found.
The TRAPPIST-1 system contains a total of seven planets, all around the size of Earth. Three of them -- TRAPPIST-1e, f and g -- dwell in their star’s so-called “habitable zone.” The habitable zone, or Goldilocks zone, is a band around every star (shown here in green) where astronomers have calculated that temperatures are just right -- not too hot, not too cold -- for liquid water to pool on the surface of an Earth-like world. 

This artist's concept appeared on the February 23rd, 2017 cover of the journal Nature announcing that the TRAPPIST-1 star, an ultra-cool dwarf, has seven Earth-size planets orbiting it. Any of these planets could have liquid water on them. Planets that are farther from the star are more likely to have significant amounts of ice, especially on the side that faces away from the star.

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The new findings were published in a study on Wednesday in the journal Nature, and were also announced during a news conference at NASA Headquarters in Washington.

"This is the first time that so many planets of this kind are found around the same star," continued Zurbuchen.

Zurbuchen called the discovery crucial in inching science closer to answering the question "are we alone out there?"

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"What we really have in this story is a major step forward toward answering one of these very questions that are at the heart of so many of our philosophers... basically are we alone out there?"

"We are making a leap forward, in fact, toward answering that question."

Thousands of planets outside of our solar system, known as exoplanets, have been found in recent years, but few have existed in conditions that scientists predict could foster life.

Last year, astronomers discovered an Earth-like planet orbiting Proxima Centauri, the next closest star to our own solar system, which rests about four light-years away.

Lead author of new study Michaël Gillon described the TRAPPIST planetary system as "amazing" and not "only because we found so many planets but because they are all surprisingly similar in size to Earth."

All seven of the newly found stars are closer to their star than Mercury is to our sun. In our solar system, that would make the planets too hot to host liquid water -- considered one of the fundamental building blocks for life at this point.

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But TRAPPIST-1 is a red dwarf, which makes it much cooler than our sun.

"TRAPPIST-1 is much cooler and much smaller than our Sun, and so the planets in its habitable zone are much closer to it," said Gillon.

Scientists also suspect the planets may be tidally-locked to the star, which would mean the same side of the planet faces its sun at all times, just like the same side of the moon permanently faces Earth. For the planets, this condition would mean one side of the planet is permanently light while the other permanently dark. It would also likely mean a significant temperate variation from one side to the other.

The next big question scientists hope to answer is whether or not the exoplanets have atmosphere.

"NASA's Hubble Space Telescope has initiated the screening of four of the planets, including the three inside the habitable zone," according to a NASA press release. "These observations aim at assessing the presence of puffy, hydrogen-dominated atmospheres, typical for gaseous worlds like Neptune, around these planets."

RELATED: Check out artist's renderings of another exoplanet

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Exoplanet Proxima b
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Exoplanet Proxima b
A view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to our Solar System, is seen in an undated artist's impression released by the European Southern Observatory August 24, 2016. ESO/M. Kornmesser/Handout via Reuters THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. IT IS DISTRIBUTED, EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS
The planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to our Solar System, is seen in an undated artist's impression released by the European Southern Observatory August 24, 2016. ESO/M. Kornmesser/Handout via Reuters THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. IT IS DISTRIBUTED, EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS
A view of the southern skies over the European Southern Observatory (ESO) 3.6-metre (11.8 foot) telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope as seen in an undated image released by the European Southern Observatory August 24, 2016. Y. Beletsky/LCO/ESO/ESA/NASA/M. Zamani/Handout via Reuters THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. IT IS DISTRIBUTED, EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS
GERMANY - JUNE 22: Illustration taken from 'Uranometria' (1603) by Johann Bayer, showing consellations of Centaurus. Alpha Centauri is the star positioned on the front hoof of the centaur. German astronomer and lawyer Johann Bayer (1572-1625) invented the system for naming stars using letters from the Greek alphabet, a system still used today for the brighter stars - those visible to the human eye without the aid of a telescope. 'Uranometria' depicts the positions of nearly 1000 stars in addition to those identified by Tycho Brahe. Alpha Centauri is a double star and the second closest star to our own Sun, 4.35 light years away (only Proxima Centauri, a red dwarf star in the same system is closer). It is a very similar star to the Sun, leading to speculation that it could have planets harbouring life. (Photo by SSPL/Getty Images)
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