أثار اكتشاف وكالة الفضاء الدولية «ناسا»، الذي أعلنت عنه منذ دقائق، في مؤتمر صحفي حول وجود مجموعة شمسية أخرى مكونة من سبعة كواكب على الأقل جدلًا كبيرًا غير مسبوق.
إنه صغير و نجم خافت وثيق نسبيا وهو موطن لسبعة كواكب بحجم الأرض مع الظروف التي يمكن أن تكون مناسبة للماء السائل وربما حتى الحياة.
يعد الإكتشاف سجلا قياسيا لكل من معظم الكواكب التى بحجم الأرض والكواكب الأكثر تعرضا للسكن التى إكتشفت حتى الأن أكثر من أي وقت مضى حول نجم واحد.
نظام الكواكب الغريب هو نظام معقد جدا، مع كل من هذه العوالم التي تدور حول نجمها فهى أقرب من مدارات عطارد التى تدور حول الشمس، وفقا لتقرير نشر حديثا.
"لو كنت على سطح واحد من هذه الكواكب، هل ترى تلك الكواكب الأخرى كما نرى القمر، أو أصغر قليلا،" كما يقول مايكل جيلون، وهو عالم فلك في جامعة لييج في بلجيكا. "الرأي سيكون مؤثر جدا."
والرائع بالأمر،أن النجم الأحمر يبعد حوالي 40 سنة ضوئية، في كوكبة الدلو. واضاف "انها نجمة صغيرة جدا"، ويقول جيلون، "10 مرات أصغر من الشمس".
والأمر الأروع أنه حتى وقت قريب، لم يكن أحد حتى يبحث عن أية كواكب حول ما يسمى بالنجوم الأقزام .
ومع ذلك..قبل نحو عام، أعلن العلماء أن لديهم وجدت ثلاثة كواكب حول هذا النجم. وشنوا حملة لدراسة النجم الأكثر كثافة، وكان مستغربا ان نجد أربعة أكثر. ورصدت كل الكواكب من خلال البحث عن نجم معتم خافت كالذي يحدث عندما يتم حظر النجوم التي تومض عندما يمر كوكب أمام النجم.
وتلك المجموعة الشمسية التي تبعد عن الأرض بحوالي 40 سنة ضوئية، يسكن بها سبعة كواكب، حجمها مماثل لحجم الأرض، وتدور حول شمس اسمها «ترابيست 1»، وتقع ثلاثة كواكب منها في المنطقة الداعمة أو المأهولة للحياة بحسب تقرير وكالة «ناسا».
وتعد هذه هي المرة الأولى التي يُكتشف فيها العديد من الكواكب المماثلة لحجم الأرض، والتي تدور حول نفس النجم.
ويعتقد علماء «ناسا» أن هذا الاكتشاف هو خطوة نحو العثور على حياة أخرى غير الموجودة على كوكب الأرض، وسيتم التأكد إذا استطاعوا العثورعلى كل مسببات الحياة على كوكب الأرض مثل المياه، والأوكسجين، ومكونات الغلاف الجوي بشكل عام.
Astronomers Find 7 Earth-Size Planets Around A Nearby Star
NASA announces discoveries beyond our solar system
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.
A small, faint star relatively close by is home to seven Earth-size planets with conditions that could be right for liquid water and maybe even life.
The discovery sets a record for both the most Earth-size planets and the most potentially habitable planets ever discovered around a single star.
The strange planetary system is quite compact, with all of these worlds orbiting their star closer than Mercury orbits the sun, according to a newly published report in Nature.
"If you were on the surface of one of these planets, you would see the other ones as we see the moon, or a bit smaller," says Michaël Gillon, an astronomer at the University of Liège in Belgium. "The view would be very impressive."
The cool, reddish star is about 40 light-years away, in the constellation Aquarius. "It's a very tiny star," says Gillon, "10 times smaller than the sun."
Until recently, no one was even looking for planets around so-called ultracool dwarf stars.
About a year ago, however, scientists announced that they'd found three planets around this star. They launched a campaign to study the star more intensively, and were surprised to find four more. All of the planets were spotted by looking for a faint dimming that occurs when starlight is blocked by a planet passing in front of the star.
Julien de Wit of MIT, one of the astronomers on the research team, says these planets have a "winning combination" of being temperate, Earth-size and ideally suited for follow-up observations with telescopes to analyze their atmospheres.
Already, initial observations have been made with the Hubble Space Telescope, he says, and the data is being analyzed. More observations with Hubble are planned to search for signs of water or methane.
Astronomers could get an even better sense after 2018, when the next-generation James Webb Space Telescope is expected to launch. It could provide an in-depth look at the atmospheres of these planets.
Some theoreticians question whether this type of star could support life, since it is so different from the sun and the close-in planets would get hit by so much ultraviolet radiation. "We really cannot know," says Emmanuël Jehin of the University of Liège. "So it looks like everything is possible, at this point. It's very exciting."
The seven exoplanets were all 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 newresearch 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.
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.
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.
They were largely overlooked until Gillon decided to study the space around one of these dwarves.
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.
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.