"They've all experienced the same stellar history because they orbit the same star".
The study indicates that all seven planets are mostly made of rock.
Additional evidence for the seven exoplanets discovered last year around the nearby Trappist-1 star at a distance of 40 light years is now in the hands of scientists with the help of the Hubble Space Telescope. The amount varies, but some planets could potentially have more water than exists on Earth.
Sean Carey, manager of the Spitzer Science Center at Cal Tech, said, "We now know more about TRAPPIST-1 than any other planetary system apart from our own".
"When astronomers refer to life, we often mean any sort of organism, including micro-organisms and plants, which are the living beings that have most profoundly changed the chemistry of our atmosphere".
"All the traffic lights we have passed so far are green".
By not detecting the presence of a large abundance of hydrogen in the planets' atmospheres, Hubble is helping to pave the way for NASA's James Webb Space Telescope, scheduled to launch in 2019. Cosmologists affirmed it's seven conceivably livable planets in mid-2017 utilizing the NASA Spitzer Space Telescope and the European Southern Observatory's La Silla Observatory in Chile. The first updated the planets radii, giving us more accurate physical measurements.
Trappist-1 is named after the Transiting Planets and Planetesimals Small Telescope (Trappist) in Chile, which discovered the first two planets in the system.
It was also found that TRAPPIST is up to twice as old as our solar system - between 5.4 and 9.8 billion years.
A related study by a team using the Hubble Space Telescope peered into the atmospheres of TRAPPIST-1d, e, f and g.
GettyThe planets are believed to be rocky in the same way as Earth and orbit a red-dwarf star
The measurements of the densities, when combined with models of the planets' compositions, strongly suggest that the seven TRAPPIST-1 planets are not barren rocky worlds, researchers said. By comparison, our Earth's oceans account for only 0.02 percent of our planet's mass.
As a result the seven planets are all nearer their star than Mercury is to the sun, yet enjoy relatively mild climates. The lack of hydrogen in their atmospheres further supports theories about the planets being terrestrial in nature.
Co-author Professor Brice-Olivier Demory, from the University of Bern in Germany, said: "Our study is an important step forward as we continue to explore whether these planets could support life". They may also be tidally locked, meaning the same side of the planet is always facing the star, and each side is in perpetual day or night.
The discovery of the TRAPPIST-1 system past year generated a lot of excitement. Although the planets are all closer to their star than Mercury is to the Sun, TRAPPIST-1 is such a cool star that its planets are temperate.
To get the density, scientists take advantage of what is called "transit timing variations". Because the TRAPPIST-1 planets are all squashed in so closely, their gravitational pulls can mess with each other's orbits. Those varieties in orbital planning are utilized to appraise the planets' masses.
It may have a denser iron core, and it does not necessarily have a thick atmosphere, ocean or ice layer.
TRAPPIST-1e is the rockiest planet of them all but still is believed to have the potential to host some liquid water, said the study published in the journal Astronomy and Astrophysics. It's the most similar to Earth, in size, density and the amount of radiation it receives from its star.
TRAPPIST-1f, g and h are far enough from the host star that water could be frozen as ice across these surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules that we find on Earth, such as carbon dioxide.
Having a better idea of each planet's radius and mass, as well as new information about the star itself, should give scientists a greater understanding of each planet's density.
"Oxygen is not required for life to exist, however, if present oxygen gas is useful to reveal that biological processes such as photosynthesis are active", said Dr Amaury Triaud.