(CNN) Astronomers have found at least seven Earth-sized planets orbiting the same star 40 light-years away, according to a study published Wednesday in the journal Nature. The findings were also announced at a news conference at NASA Headquarters in Washington.

This discovery outside of our solar system is rare because the planets have the winning combination of being similar in size to Earth and being all temperate, meaning they could have water on their surfaces and potentially support life.

"This is the first time that so many planets of this kind are found around the same star," said Michaël Gillon, lead study author and astronomer at the University of Liège in Belgium.

The seven exoplanets wereall found in tight formation around an ultracool dwarf star called TRAPPIST-1 . Estimates of their mass also indicate that they are rocky planets, rather than being gaseous like Jupiter. Three planets are in the habitable zone of the star, known as TRAPPIST-1e, f and g, and may even have oceans on the surface.

The TRAPPIST-1 star, an ultracool dwarf, has seven Earth-size planets orbiting it.

The researchers believe that TRAPPIST-1f in particular is the best candidate for supporting life. It's a bit cooler than Earth, but could be suitable with the right atmosphere and enough greenhouse gases.

If TRAPPIST-1 sounds familiar, that's because these researchers announced the discovery of three initial planets orbiting the same star in May. The new research increased that number to seven planets total.

"I think we've made a crucial step towards finding if there is life out there," said Amaury Triaud, one of the study authors and an astronomer at the University of Cambridge. "I don't think any time before we had the right planets to discover and find out if there was (life). Here, if life managed to thrive and releases gases similar to what we have on Earth, we will know."

Life may begin and evolve differently on other planets, so finding the gases that indicate life is key, the researchers added.

"This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life," said Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate. "Answering the question 'are we alone?' is a top science priority, and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal."

And as we've learned from studying and discovering exoplanets before, where there is one, there are more, said Sara Seager, professor of planetary science and physics at Massachusetts Institute of Technology. Seager and other researchers are encouraged by the discovery of this system because it improves our chances of finding another habitable planet, like Earth, in the future, by knowing where to look.

What we know

The planets are so close to each other and the star that there are seven of them within a space five times smaller than the distance from Mercury to our sun. This proximity allows the researchers to study the planets in depth as well, gaining insight about planetary systems other than our own.

The seven planets of TRAPPIST-1 compared with Mercury, Venus, Earth and Mars.

Starting closest to the star and moving out, the planets have respective orbits from one and a half to nearly 13 Earth days. The orbit of the farthest planet is still unknown.

Standing on the surface of one of the planets, you would receive 200 times less light than you get from the sun, but you would still receive just as much energy to keep you warm since the star is so close. It would also afford some picturesque views, as the other planets would appear in the sky as big as the moon (or even twice as big).

On TRAPPIST-1f, the star would appear three times as big as the sun in our sky. And because of the red nature of the star, the light would be a salmon hue, the researchers speculate.

The researchers believe the planets formed together further from the star. Then, they moved into their current lineup. This is incredibly similar Jupiter and its Galilean moons.

Like the moon, the researchers believe the planets closest to the star are tidally locked. This means that the planets always face one way to the star. One side of the planet is perpetually night, while the other is always day.

What the TRAPPIST-1 planetary system may look like.

Based on preliminary climate modeling, the researchers believe that the three planets closest to the star may be too warm to support liquid water, while the outermost planet, TRAPPIST-1h, is probably too distant and cold to support water on the surface. But further observation is needed to know for sure.

How the discovery was made

TRAPPIST-1 barely classifies as a star at half the temperature and a tenth the mass of the sun. It is red, dim and just a bit larger than Jupiter. But these tiny ultracool dwarf stars are common in our galaxy.

Photos: Weird and wonderful planets beyond our solar system Photos: Weird and wonderful planets beyond our solar system For the first time, an exoplanet has been found orbiting a dead star known as a white dwarf. In this artist's illustration, the Jupiter-sized planet WD 1856 b orbits the white dwarf every day and a half. Hide Caption 1 of 67 Photos: Weird and wonderful planets beyond our solar system This illustration shows a carbon-rich planet with diamond and silica as ts main minerals. Water can convert a carbon-rich planet into one that's made of diamonds. In the interior, the main minerals would be diamond and silica (a layer with crystals in the illustration). The core (dark blue) might be made of an iron-carbon alloy. Hide Caption 2 of 67 Photos: Weird and wonderful planets beyond our solar system This image shows a young sun-like star being orbited by two gas giant exoplanets. It was taken by the SPHERE instrument on European Southern Observatory's Very Large Telescope. The star can be seen in the top left corner, and the planets are the two bright dots. Hide Caption 3 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's impression shows a Neptune-sized planet in the Neptunian Desert. It is extremely rare to find an object of this size and density so close to its star. Hide Caption 4 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's impression of the multiplanetary system of newly discovered super-Earths orbiting a nearby red dwarf star called Gliese 887. Hide Caption 5 of 67 Photos: Weird and wonderful planets beyond our solar system The newly discovered exoplanet AU Mic b is about the size of Neptune. Hide Caption 6 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Proxima b is a little more massive than the Earth. Hide Caption 7 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's illustration of an exoplanet's atmosphere with a white dwarf star visible on the horizon. The starlight of a white dwarf filtered through the atmosphere of an exoplanet that's orbiting it could reveal if the planet has biosignatures. Hide Caption 8 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's illustration of the Kepler-88 planetary system, where one giant exoplanet and two smaller planets orbit the Kepler-88 star. The system is more than 1,200 light-years away. Hide Caption 9 of 67 Photos: Weird and wonderful planets beyond our solar system This is an illustration of newly discovered exoplanet Kepler-1649c orbiting around its host red dwarf star. Hide Caption 10 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's illustration shows the night-side view of the exoplanet WASP-76b, where iron rains down from the sky. Hide Caption 11 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's concept of a ringed planet passing in front of its host star. It shows how "puffy" a ringed planet may look to us from afar. Hide Caption 12 of 67 Photos: Weird and wonderful planets beyond our solar system The sizes of the 17 new planet candidates, seen here in orange, are compared to colorized representations of Mars, Earth and Neptune. The green planet is KIC-7340288 b, a rocky planet in the habitable zone of its star. Hide Caption 13 of 67 Photos: Weird and wonderful planets beyond our solar system Artist's impression of K2-18b. CREDIT Amanda Smith Hide Caption 14 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's illustration a massive planet orbiting a cool, young star. In the case of the newly discovered system, the planet is 10 times more massive than Jupiter, and the orbit of the planet is nearly 600 times that of Earth around the sun. Hide Caption 15 of 67 Photos: Weird and wonderful planets beyond our solar system Welcome to the KELT-9 system. The host star is a hot, rapidly rotating A-type star that is about 2.5 times more massive and almost twice as hot as our sun. The hot star blasts its nearby planet KELT-9b with massive amounts of radiation, leading to a daylight temperature of 7800 degrees Fahrenheit, hotter that most stars and only 2000 degrees cooler than the sun. Hide Caption 16 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's rendering of the Proxima Centauri planetary system. The newly discovered super-Earth exoplanet Proxima c, on the right, has an orbit of about 5.2 Earth years around its host star. The system also comprises the smaller Proxima b, on the left, discovered in 2016. Illustration by Lorenzo Santinelli. Hide Caption 17 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's concept of GJ180d, the nearest temperate super-Earth to us with the potential to support life. Hide Caption 18 of 67 Photos: Weird and wonderful planets beyond our solar system An illustration of WASP-12b as it spirals in a death dance towards its star. The planet will meet its end in three million years. Hide Caption 19 of 67 Photos: Weird and wonderful planets beyond our solar system TOI 700 d is the first potentially habitable Earth-size planet spotted by NASA's planet-hunting TESS mission. Hide Caption 20 of 67 Photos: Weird and wonderful planets beyond our solar system TOI 1338 b is silhouetted by its two host stars, making it the first such discovery for the TESS mission. TESS only detects transits from the larger star Hide Caption 21 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's illustration shows a wet exoplanet with an oxygen atmosphere. The red sphere is the M-dwarf star the exoplanet orbits. Hide Caption 22 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's illustration shows a dry exoplanet with an oxygen atmosphere. The red sphere is the M-dwarf star the exoplanet orbits. Hide Caption 23 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's illustration of the Kepler 51 system shows newly discovered super-puff exoplanets, which are also called "cotton candy" exoplanets because they're so lightweight. Hide Caption 24 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's concept illustration shows an exoplanet with two moons orbiting within the habitable zone of a red dwarf star. Hide Caption 25 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's illustration of two exoplanets colliding in a binary star system. Hide Caption 26 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's illustration of a Neptune-type exoplanet in the icy outer reaches of its star system. It could look something like a large, newly discovered gas giant that takes about 20 years to orbit a star 11 light years away from Earth. Hide Caption 27 of 67 Photos: Weird and wonderful planets beyond our solar system This image shows a comparison of red dwarf star GJ 3512 to our solar system, as well as other nearby red-dwarf planetary systems. Hide Caption 28 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's illustration showcases exoplanet K2-18b orbiting its host star. It's currently the only super-Earth exoplanet that has water vapor in its atmosphere and could be within the right temperature to support life. Hide Caption 29 of 67 Photos: Weird and wonderful planets beyond our solar system This is an illustration of an exomoon losing mass as it's being pulled around the gas giant it orbits. Hide Caption 30 of 67 Photos: Weird and wonderful planets beyond our solar system An illustration shows what the orbit of exoplanet HR 5183 b would look like if it was dropped down in our solar system. It would likely swing from the asteroid belt to out past Neptune, the eighth planet in our solar system. Hide Caption 31 of 67 Photos: Weird and wonderful planets beyond our solar system At least two giant planets, aged 20 million years at most, orbit the Beta Pictoris star. A disk of dust and gas surrounding the star can be seen in the background. Hide Caption 32 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's interpretation of what super-Earth GJ 357 d might look like. It lies within the habitable zone of its star which is 31 light-years from Earth. Hide Caption 33 of 67 Photos: Weird and wonderful planets beyond our solar system An artist's impression of a circumplanetary disk around PDS 70 c, a gas giant exoplanet in a star system 370 light-years away. Hide Caption 34 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's illustration shows two gas giant exoplanets orbiting the young star PDS 70. These planets are still growing by gathering material from a surrounding disk. In the process, they have gravitationally carved out a large gap in the disk. Hide Caption 35 of 67 Photos: Weird and wonderful planets beyond our solar system An artist's illustration of HD 21749c, the first Earth-size planet found by TESS, as well as its sibling, HD 21749b, a warm mini-Neptune. Hide Caption 36 of 67 Photos: Weird and wonderful planets beyond our solar system A "hot Saturn" passes in front of its host star in this illustration. Astronomers who study stars used "starquakes" to characterize the star, which provided critical information about the planet. Hide Caption 37 of 67 Photos: Weird and wonderful planets beyond our solar system Artist's concept of TESS against background of stars & orbiting planets in the Milky Way. Credit: ESA, M. Kornmesser (ESO), Aaron E. Lepsch (ADNET Systems Inc.), Britt Griswold (Maslow Media Group), NASA's Goddard Space Flight Center & Cornell University Hide Caption 38 of 67 Photos: Weird and wonderful planets beyond our solar system A super-telescope made the first direct observation of an exoplanet using optical interferometry. This method revealed a complex exoplanetary atmosphere with clouds of iron and silicates swirling in a planet-wide storm. The technique presents unique possibilities for characterizing many of the exoplanets known today. Hide Caption 39 of 67 Photos: Weird and wonderful planets beyond our solar system This image shows an artist's impression of the surface of Barnard's star b, a cold Super-Earth discovered orbiting Barnard's star 6 light-years away. Hide Caption 40 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's illustration shows newly discovered exoplanet K2-288Bb, 226 light-years away and half the size of Neptune. It orbits the fainter member of a pair of cool M-type stars every 31.3 days. Hide Caption 41 of 67 Photos: Weird and wonderful planets beyond our solar system This is an artist's impression of the exoplanet HAT-P-11b. The planet has an extended helium atmosphere that's being blown away by the star, an orange dwarf star smaller but more active than our sun. Hide Caption 42 of 67 Photos: Weird and wonderful planets beyond our solar system An artist's illustration of what the super-Earth found around the orange-hued star HD 26965 (also known as 40 Eridani A) might look like. The recently discovered exoplanet is being compared to the fictional planet of Vulcan because Star Trek creator Gene Roddenberry said the star was the ideal candidate to host Vulcan, Mr. Spock's home world. Hide Caption 43 of 67 Photos: Weird and wonderful planets beyond our solar system The TRAPPIST-1 star, an ultra-cool dwarf, has seven Earth-size planets orbiting it. Hide Caption 44 of 67 Photos: Weird and wonderful planets beyond our solar system For the first time, eight planets have been found orbiting another star, tying with our solar system for the most known planets around a single star. The Kepler-90 system is in the constellation Draco, more than 2,500 light-years from Earth. Hide Caption 45 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's illustration shows exoplanet Ross 128 b, with its red dwarf host star in the background. The planet is only 11 light-years from our solar system. It is now the second-closest temperate planet to be detected, after Proxima b. Hide Caption 46 of 67 Photos: Weird and wonderful planets beyond our solar system WASP-121b, 880 light-years away, is considered a hot Jupiter-like planet. It has a greater mass and radius than Jupiter, making it "puffier." If WASP-121b were any closer to its host star, it would be ripped apart by the star's gravity. Hide Caption 47 of 67 Photos: Weird and wonderful planets beyond our solar system NASA's Kepler space telescope team has identified 219 more planet candidates, 10 of which are near-Earth size and in the habitable zone of their stars. Hide Caption 48 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's concept shows OGLE-2016-BLG-1195Lb, a planet orbiting an incredibly faint star 13,000 light-years away from us. It is an "iceball" planet with temperatures reaching minus-400 degrees Fahrenheit. Hide Caption 49 of 67 Photos: Weird and wonderful planets beyond our solar system LHS 1140b is located in the liquid water habitable zone surrounding its host star, a small, faint red star named LHS 1140. The planet weighs about 6.6 times the mass of Earth and is shown passing in front of LHS 1140. Depicted in blue is the atmosphere the planet may have retained. Hide Caption 50 of 67 Photos: Weird and wonderful planets beyond our solar system An artist's concept image of the surface of the exoplanet TRAPPIST-1f. Of the seven exoplanets discovered orbiting the ultracool dwarf star TRAPPIST-1, this one may be the most suitable for life. It is similar in size to Earth, is a little cooler than Earth's temperature and is in the habitable zone of the star, meaning liquid water (and even oceans) could be on the surface. The proximity of the star gives the sky a salmon hue, and the other planets are so close that they appear in the sky, much like our own moon. Hide Caption 51 of 67 Photos: Weird and wonderful planets beyond our solar system Artist's conception of the binary system with three giant planets discovered, where one star hosts two planets and the other hosts the third. The system represents the smallest-separation binary in which both stars host planets that has ever been observed. Hide Caption 52 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to our solar system. Hide Caption 53 of 67 Photos: Weird and wonderful planets beyond our solar system An artist's rendering shows Earth-sized exoplanets TRAPPIST-1b and 1c in a rare double transit event as they pass in front of their ultracool red dwarf star, which allowed Hubble to take a peek at at their atmospheres. Hide Caption 54 of 67 Photos: Weird and wonderful planets beyond our solar system Out of a new discovery of 104 exoplanets, astronomers found four similar in size to Earth that are orbiting a dwarf star. Two of them have the potential to support life. The craft depicted in this illustration is the NASA Kepler Space Telescope, which has helped confirm the existence of thousands of exoplanets. Hide Caption 55 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's impression shows a view of the triple-star system HD 131399 from close to the giant planet orbiting in the system. Located about 320 light-years from Earth, the planet is about 16 million years old, making it also one of the youngest exoplanets discovered to date. Hide Caption 56 of 67 Photos: Weird and wonderful planets beyond our solar system An artistic impression of the planet Kepler-1647b, which is nearly identical to Jupiter in both size and mass. The planet is expected to be roughly similar in appearance. But it is much warmer: Kepler-1647b is in the habitable zone. Hide Caption 57 of 67 Photos: Weird and wonderful planets beyond our solar system HD-106906b is a gaseous planet 11 times more massive than Jupiter. The planet is believed to have formed in the center of its solar system, before being sent flying out to the edges of the region by a violent gravitational event. Hide Caption 58 of 67 Photos: Weird and wonderful planets beyond our solar system Kepler-10b orbits at a distance more than 20 times closer to its star than Mercury is to our own sun. Daytime temperatures exceed 1,300 degrees Celsius (2,500 degrees Fahrenheit), which is hotter than lava flows on Earth. Hide Caption 59 of 67 Photos: Weird and wonderful planets beyond our solar system This Jupiter-like planet in the HD-188753 system, 149 light-years from Earth, has three suns. The main star is similar in mass to our own Sun. The system has been compared to Luke Skywalker's home planet Tatooine in "Star Wars." Hide Caption 60 of 67 Photos: Weird and wonderful planets beyond our solar system Kepler-421b is a Uranus-sized transiting exoplanet with the longest known year, as it circles its star once every 704 days. The planet orbits an orange, K-type star that is cooler and dimmer than our Sun and is located about 1,000 light-years from Earth in the constellation Lyra. Hide Caption 61 of 67 Photos: Weird and wonderful planets beyond our solar system Astronomers discovered two planets less than three times the size of Earth orbiting sun-like stars in a crowded stellar cluster approximately 3,000 light-years from Earth in the constellation Cygnus. Hide Caption 62 of 67 Photos: Weird and wonderful planets beyond our solar system This artist's conception shows a hypothetical planet with two moons orbiting in the habitable zone of a red dwarf star. The majority of the sun's closest stellar neighbors are red dwarfs. Hide Caption 63 of 67 Photos: Weird and wonderful planets beyond our solar system Kepler-186f was the first validated Earth-sized planet to be found orbiting a distant star in the habitable zone. This zone a range of distance from a star where liquid water might pool on the planet's surface. Hide Caption 64 of 67 Photos: Weird and wonderful planets beyond our solar system Kepler-69c is a super-Earth-size planet similar to Venus. The planet is found in the habitable zone of a star like our sun, approximately 2,700 light years from Earth in the constellation Cygnus. Hide Caption 65 of 67 Photos: Weird and wonderful planets beyond our solar system The Kepler-444 system formed when the Milky Way was just 2 billion years old. The tightly packed system is home to five planets that range in size, the smallest is comparable to the size of Mercury and the largest to Venus, orbiting their sun in less than 10 days. Hide Caption 66 of 67 Photos: Weird and wonderful planets beyond our solar system This artistic concept image compares Earth, left, with Kepler-452b, which is about 60% larger. Both planets orbit a G2-type star of about the same temperature; however, the star hosting Kepler-452b is 6 billion years old -- 1.5 billion years older than our sun. Hide Caption 67 of 67

They were largely overlooked until Gillon decided to study the space around one of these dwarfs.

The researchers used a telescope called TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) to observe its starlight and changes in brightness. The team saw shadows, like little eclipses, periodically interrupting the steady pattern of starlight. This is called transiting. The shadows indicated planets, and further observation confirmed them.

In July, the team was able to determine that two of the closest planets to the stars had atmospheres that were more compact and comparable to those of Earth, Venus and Mars by observing starlight through the planets' atmosphere.

By using a global network ground-based telescopes like TRAPPIST and space-based telescopes like Spitzer, the researchers continued looking toward the TRAPPIST system and were able to determine the orbital periods, distances from their star, radius and and masses of the planets.

What's next

Over the next decade, the researchers want to define the atmosphere of each planet, as well as to determine whether they truly do have liquid water on the surface and search for signs of life.

Although 40 light-years away doesn't sound too far, it would take us millions of years to reach this star system. But from a research perspective, it's a close opportunity and the best target to search for life beyond our solar system.

"If we learn something now, it can determine if we looked in the right place," Gillon said.

In 2018, the James Webb Space Telescope will launch and be positioned 1 million miles from Earth with an unprecedented view of the universe. It can observe large exoplanets and detect starlight filtered through their atmosphere.

The researchers are also searching for similar star systems to conduct more atmospheric research. Four telescopes named SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) based in Chile will survey the southern sky for this purpose.

This star system will probably outlive us because this type of star evolves so slowly. When our sun dies, TRAPPIST-1 will still be a young star and will live for another trillion years, Gillon said. After we are gone, if there is another part of the universe for life to carry on, it may be in the TRAPPIST-1 system.

"This is the most exciting result I have seen in the 14 years of Spitzer operations," said Sean Carey, manager of NASA's Spitzer Science Center at Caltech/IPAC in Pasadena, California. "Spitzer will follow up in the fall to further refine our understanding of these planets so that the James Webb Space Telescope can follow up. More observations of the system are sure to reveal more secrets."