A total of seven rocky planets very similar to Earth have been observed in orbit around a dwarf star just 40 light years away. At least three out of seven planets are in the star’s habitable zone, where there can be water – and thus life.
There are at least seven exoplanets in orbit around the star, which ‘only’ lie 40 light years from Earth, and they are all roughly the same size as our own blue planet. (Source: ESO / M. Grain Knives / spaceengine.org )Charlotte Price PerssonJournalist February 22, 2017ASTRONOMY
Last year, astronomical orbits were furious when a research team discovered three planets of roughly the same size and temperature as Venus and Earth orbiting the same star. Back then, they were judged to be the best candidates so far to search for life outside the solar system, though only one of them immediately had the potential to be within the star’s habitable zone.Story short
- 4 new planets have been found orbiting a star in our astronomical backyard.
- We now know a total of 7 planets in this system, of which at least 3 are in the ‘habitable zone’ where there can be water – and thus – life on the planets. It has never been seen before.
Now, the same scientists have discovered another four Earth-like planets – orbiting the same star as the first three. At least three of the seven planets are at a distance from their star so that they can potentially have surface water and thus, perhaps, life. The orbit of the last planet remains unclear.
“I was about to fall down the chair when I heard that they had found 4 more planets. We have never seen so many Earth-like planets so close to their star or so many planets in the habitable zone around the same star, ”says Danish astrophysicist Lars Buchhave, who works at the Niels Bohr Institute at the University of Copenhagen.
He has not been included in the new study , but had heard beforehand about the results, which have just been published on the cover of the acclaimed journal Nature.
Join us on a journey from Earth beyond the Moon to the star TRAPPIST-1, located in the constellation Aquarius. The little ultra-cold dwarf star TRAPPIST-1 is so weak that it would be impossible to see with the eye alone for the imaginary space traveler until we get very close. At that distance, the seven exoplanets will also be visible.
At least three planets may have water
The seven planets are all extraordinarily close to their star, TRAPPIST-1, and at least three of them are in the habitable zone, also called the Gold Lock zone. The habitable zone denotes the distance a planet has to lie from its star in order for liquid water to be on the surface, and it varies depending on how large and hot the star is. It is crucial for the temperature of the planets.
On the ‘glass plate’ here are placed both the star TRAPPIST-1 and its seven exoplanets. There is water, frost and steam next to the planets where it fits the conditions. This image is front page of the journal Nature February 22, 2017. (Source: NASA / R. Hurt / T. Pyle)
The star of the new studio is a so-called ultra-cold dwarf star, which – as the name indicates – is a pretty small and cold star. In fact, its temperature is only half that of the Sun, and its mass, ie weight, under one tenth of our sun. Therefore, the habitable zone is also very close to the star.
»All seven planets have extremely short orbits around the star; the longest is only about 20 days. In comparison, the inner planet of our own solar system, Mercury, has an orbit of 88 days on the Sun. This is an extremely compact system, “explains Lars Buchhave.
Very similar to the Earth
In the new study, scientists have also – quite extraordinarily – succeeded in determining the mass of the planets, and so they can say that the six innermost planets are very likely to be made of rock material. When you have the radius of the planets, which are measured from the star’s dive as they pass through it, you can use mass to calculate the density.
The density, that is, the density of the planet, reveals whether it is a gas planet such as Jupiter or a rock planet like Earth.The TRAPPIST-1 system is special because:
- It is unique to see so many planets in such close orbit around their star. All seven planets could easily float around the Sun within Mercury’s orbit if they were put into our own solar system.
- Never before have so many planets been observed within the habitable zone around a single star.
- It is the largest known number of new worlds that can have liquid water on the surface, about a single star.
- All seven planets are the size of the Earth plus minus 10-20 percent. It differs markedly from the planets in our own solar system. However, several planets can hide further out.
- This is the first time that planets have been found by a dwarf star .
“This is an absolutely fantastic planetary system – not only because we have found so many planets, but also because they are all astonishingly similar to Earth,” says head author Michaël Gillon of the STAR Institute at the University of Liège, Belgium.
Normally, nothing can be said about mass for such small planets, but it has succeeded because the system is so compact, explains Lars Buchhave.
“They can measure how much the gravitational forces of the planets pull into each other and from there make a model that reveals mass. The planets then turn out to be rocky, and that’s to be expected – since small planets have a hard time holding on to a gaseous atmosphere – but here we actually have a measurement to confirm that. “
The first time dwarf stars are examined
The extraordinary planetary system was initially detected using the ESO telescope TRAPPIST, located at La Silla Observatory in Chile.
However, it has subsequently been observed by a series of different telescopes on Earth and in space – including NASA’s space observatory, the Spitzer telescope.
Five facts about the seven Earth-like exoplanets found in orbit of the nearby star TRAPPIST-1; from their rocky planet structure to the possibility of liquid water. (Source: ESO)
“This is the first time someone is investigating these very small and cold stars. They simply went after them specifically in this study to find out if there are small planets around them, partly because observations from NASA’s spacecraft Kepler suggested it, “says Lars Buchhave.
“We knew well that m dwarfs, as they are called, probably had many planets and also some in the habitable zone, but that this one actually has seven planets with three in the habitable zone, I didn’t expect that,” he continues. .The star …
- Has a mass of 8 percent of the Sun’s mass.
- Lights only with 0.05 percent of the Sun’s radiation.
- Has a surface temperature of 2,559 degrees against the Sun’s 5,780 degrees on the surface.
- Named TRAPPIST-1 because it is the first dwarf star with planets around it, the research team mocks.
- Is much colder and redder in color than the Sun and only slightly larger than the planet Jupiter.
Lots of new worlds to explore
Astrophysicist Emmanuël Jehin, who co-authored the study and also works at the University of Liège, explains that the studies with TRAPPIST are a precursor to an even more ambitious project called SPECULOOS, housed at ESO’s Paranal Observatory.
“We are building a new telescope that will take a closer look at these types of stars and their planets. We will find many more systems like this, I have no doubt at all, ”says Emmanuël Jehin at a teleconference organized by Nature.
“One of the great things about this discovery, where we have looked specifically at dwarf stars that no one before us has done, is that it suggests that there are many Earth-like planets close to us. For just one dwarf star, we have plenty of possible new worlds to explore, ”he continues.
Top: This is what the seven exoplanets in the orbit of TRAPPIST-1 might look like. There are numbers of sizes and orbits for the seven planets, all of roughly the same size as the Earth. Bottom: Solar system rock planets. (Source: NASA)
Future opportunities to find water
Researchers are already fully investigating the composition of the planets’ atmospheres to determine if they actually have the conditions for life, explains Emanuel Jehin.
»Methane, CO2 and oxygen are all strong indicators of life, but finding oxygen is not enough. It requires a combination, ”he says, pointing out that the opportunities to make detailed studies of the chemical compositions will be significantly improved when the Hubble Space Telescope, the James Webb telescope, is launched into space in 2018 and when the ESAs’ Extremely Large Telescope ‘is done. At that time it will also be possible to find any water on the planets.
There are immediately more problems in imagining life on the planets around TRAPPIST-1, and only through closer observation of the atmospheres can scientists say anything about what it means for possible living conditions.
TRAPPIST-1 has a diameter of 11 percent of that of the Sun. Dwarf stars are the most common stars, accounting for up to 80 percent of the Milky Way’s stars, and the ultra-cool dwarf stars are just one type in the larger category. (Source: ESO)
Unpleasant conditions: Plasma, UV radiation and perpetual cold
The problems include, for example, that dwarf stars are large consumers of so-called ‘flares’, bursts of plasma that are sent out from the surface at high speed. Such outbreaks from our own sun are currently considered. as one of the greatest threats to humanity. Dwarf stars also emit large amounts of UV radiation, which is fatal to humans.
There is also the fact that the planets appear to be ‘locked’ in which side they face their star – that is, there is always a side that is hot and one that is cold. It’s called ‘bottom rotation’.
“If we took the Earth and placed it around such a star, it wouldn’t be good. It would not be favorable conditions for our lifestyles, but who knows, maybe it will be for others? ”Says Lars Buchhave, who, however, emphasizes that this is a mere guesswork.
Have no idea if there can be life
In other words, scientists have no idea whether life can arise – and survive – around an ultra-cold dwarf star, such as they, for good reasons, can be sure it can about a star like our sun. But they also don’t figure it out until they investigate, says a third of the study’s authors, astrophysicist Amaury Triaud.
Comparison of the orbits of newly discovered exoplanets with Jupiter’s moons and with the interior of the Solar System. All the planets around TRAPPIST-1 orbit about their star much more closely than Mercury orbits the Sun, but their star is weaker, so they get roughly the same amount of radiation and heat that Venus, Earth and Mars do in the Solar System. (Source: ESO / O. Enterprises)
And a planetary system like this is a really good place to start, because the planets are so close to their star, which is very bright, and therefore causes a very large dive in the light as they pass it in their so-called ‘transit’.
“We don’t know how life develops elsewhere in the universe. On the other hand, we know that these are the most common stars found, so if we start here – where our technology actually enables us to investigate them – we can get started right away. If we find something, we’ve done it as quickly as it could, and if not, we’ve learned something important about the rise of life, “says Amaury Triaud, who works at the University of Cambridge.
Focus less on Earth
Perhaps we should generally refrain from focusing so much on Earth when thinking about conditions for life in space, reads the closing comment from Lars Buchhave:
“It is important to keep the possibilities open and explore the atmosphere of these planets, even if they orbit a very different star than the Sun. The biggest findings in science have always come from the unexpected. “