The Alpha Centauri star system is ideal to search for habitable planets by various observing techniques due to its proximity and wide range of stellar masses. Following the recent discovery of an Earth-size planet candidate located inside the Proxima Centauri habitable zone, Dr. Marois will discuss this remarkable discovery and the planet’s potential to find life. He will also present our current instrument project for the Gemini South observatory, TIKI, to discover similar planets around the two Sun-like pair located 15,000 AU from Proxima Centauri. The Alpha Centauri system is the prime target of the Breakthrough Starshot program, a project to send small quarter-size probes to take resolve images of these new worlds, and to prepare for Humanity’s first step into a new star system.
More about Dr. Marois:
Dr Marois completed his Ph.D. at the Université de Montréal in 2004. The main topic of his thesis work was to understand the limits in exoplanet imaging and to design innovating observing strategies. After his thesis, he did postdoctoral researches at the Lawrence Livermore National Laboratory, Univ. of California Berkeley and NRC. In 2008, while at NRC, he led the team that took the first image of another planetary system (HR 8799) using the Keck and Gemini telescopes. He is currently pursuing his research at the NRC Herzberg where he is part of the Gemini Planet Imager campaign, and leading the development of instruments for imaging Earth-like planets at Gemini South and at the TMT.
Here is a video of the NASA panel discussion of the findings by an international team of the TRAPPIST-1 star system with 7 earth sized exoplanets (see earlier posting here).
The briefing participants included:
Thomas Zurbuchen, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington
Michael Gillon, astronomer at the University of Liege in Belgium
Sean Carey, manager of NASA’s Spitzer Science Center at Caltech/IPAC, Pasadena, California
Nikole Lewis, astronomer at the Space Telescope Science Institute in Baltimore
Sara Seager, professor of planetary science and physics at Massachusetts Institute of Technology, Cambridge
This artist’s impression shows the view from the surface of one of the planets in the TRAPPIST-1 system. At least seven planets orbit this ultra cool dwarf star 40 light-years from Earth and they are all roughly the same size as the Earth. They are at the right distances from their star for liquid water to exist on the surfaces of several of them. This artist’s impression is based on the known physical parameters for the planets and stars seen, and uses a vast database of objects in the Universe. [Full size image]Astronomers have found a system of seven Earth-sized planets just 40 light-years away. Using ground and space telescopes, including ESO’s Very Large Telescope, the planets were all detected as they passed in front of their parent star, the ultracool dwarf star known as TRAPPIST-1. According to the paper appearing today in the journal Nature, three of the planets lie in the habitable zone and could harbour oceans of water on their surfaces, increasing the possibility that the star system could play host to life. This system has both the largest number of Earth-sized planets yet found and the largest number of worlds that could support liquid water on their surfaces.
Astronomers using the TRAPPIST–South telescope at ESO’s La Silla Observatory, the Very Large Telescope (VLT) at Paranal and the NASA Spitzer Space Telescope, as well as other telescopes around the world [1], have now confirmed the existence of at least seven small planets orbiting the cool red dwarf star TRAPPIST-1[2]. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes similar to Earth [3].
This diagram compares the sizes of the newly-discovered planets around the faint red star TRAPPIST-1 with the Galilean moons of Jupiter and the inner Solar System. All the planets found around TRAPPIST-1 are of similar size to the Earth. [Full size image.]Dips in the star’s light output caused by each of the seven planets passing in front of it — events known as transits — allowed the astronomers to infer information about their sizes, compositions and orbits [4]. They found that at least the inner six planets are comparable in both size and temperature to the Earth.
This diagram shows the changing brightness of the ultra cool dwarf star TRAPPIST-1 over a period of 20 days in September and October 2016 as measured by NASA’s Spitzer Space Telescope and many other telescopes on the ground. On many occasions the brightness of the star drops for a short period and then returns to normal. These events, called transits, are due to one or more of the star’s seven planets passing in front of the star and blocking some of its light. The lower part of the diagram shows which of the system’s planets are responsible for the transits. [Full size image]
Lead author Michaël Gillon of the STAR Institute at the University of Liège in Belgium is delighted by the findings:
“This is an amazing planetary system — not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!”
With just 8% the mass of the Sun, TRAPPIST-1 is very small in stellar terms — only marginally bigger than the planet Jupiter — and though nearby in the constellation Aquarius (The Water Carrier), it appears very dim. Astronomers expected that such dwarf stars might host many Earth-sized planets in tight orbits, making them promising targets in the hunt for extraterrestrial life, but TRAPPIST-1 is the first such system to be found.
Co-author Amaury Triaud expands:
“The energy output from dwarf stars like TRAPPIST-1 is much weaker than that of our Sun. Planets would need to be in far closer orbits than we see in the Solar System if there is to be surface water. Fortunately, it seems that this kind of compact configuration is just what we see around TRAPPIST-1!”
The team determined that all the planets in the system are similar in size to Earth and Venus in the Solar System, or slightly smaller. The density measurements suggest that at least the innermost six are probably rocky in composition.
This infographic displays some artist’s illustrations of how the seven planets orbiting TRAPPIST-1 might appear — including the possible presence of water oceans — alongside some images of the rocky planets in our Solar System. Information about the size and orbital periods of all the planets is also provided for comparison; the TRAPPIST-1 planets are all approximately Earth-sized. [Full sized image]The planetary orbits are not much larger than that of Jupiter’s Galilean moon system, and much smaller than the orbit of Mercury in the Solar System. However, TRAPPIST-1’s small size and low temperature mean that the energy input to its planets is similar to that received by the inner planets in our Solar System; TRAPPIST-1c, d and f receive similar amounts of energy to Venus, Earth and Mars, respectively.
This diagram compares the orbits of the newly-discovered planets around the faint red star TRAPPIST-1 with the Galilean moons of Jupiter and the inner Solar System. All the planets found around TRAPPIST-1 orbit much closer to their star than Mercury is to the Sun, but as their star is far fainter, they are exposed to similar levels of irradiation as Venus, Earth and Mars in the Solar System. [Full size image ]All seven planets discovered in the system could potentially have liquid water on their surfaces, though their orbital distances make some of them more likely candidates than others. Climate models suggest the innermost planets, TRAPPIST-1b, c and d, are probably too hot to support liquid water, except maybe on a small fraction of their surfaces. The orbital distance of the system’s outermost planet, TRAPPIST-1h, is unconfirmed, though it is likely to be too distant and cold to harbour liquid water — assuming no alternative heating processes are occurring [5]. TRAPPIST-1e, f, and g, however, represent the holy grail for planet-hunting astronomers, as they orbit in the star’s habitable zone and could host oceans of surface water [6].
This diagram compares the orbits of the newly-discovered planets around the faint red star TRAPPIST-1 with the Galilean moons of Jupiter and the inner Solar System. All the planets found around TRAPPIST-1 orbit much closer to their star than Mercury is to the Sun, but as their star is far fainter, they are exposed to similar levels of irradiation as Venus, Earth and Mars in the Solar System. [Full size image]These new discoveries make the TRAPPIST-1 system a very important target for future study. The NASA/ESA Hubble Space Telescope is already being used to search for atmospheres around the planets and team member Emmanuël Jehin is excited about the future possibilities:
This video takes the viewer on a quick trip from Earth, past the Moon and far beyond. We finally arrive at the faint red ultracool dwarf star TRAPPIST-1, which has a remarkable seven planets orbiting it, all having sizes similar to the Earth.
The stars in the animation are accurately positioned as in reality. The tiny ultracool dwarf TRAPPIST-1 is so dim that it would remain invisible to the naked eye until the imaginary traveller gets very close, when its seven orbiting planets can also be seen.
The artist’s impression in this video is based on the known physical parameters for the planets and stars seen, and uses a vast database of objects in the Universe. Credit: ESO/L. Calçada/spaceengine.org
[2] TRAPPIST–South (the TRAnsiting Planets and PlanetesImals Small Telescope–South) is a Belgian 0.6-metre robotic telescope operated from the University of Liège and based at ESO’s La Silla Observatory in Chile. It spends much of its time monitoring the light from around 60 of the nearest ultracool dwarf stars and brown dwarfs (“stars” which are not quite massive enough to initiate sustained nuclear fusion in their cores), looking for evidence of planetary transits. TRAPPIST–South, along with its twin TRAPPIST–North, are the forerunners to the SPECULOOS system, which is currently being installed at ESO’s Paranal Observatory.
[3] In early 2016, a team of astronomers, also led by Michaël Gillon announced the discovery of three planets orbiting TRAPPIST-1. They intensified their follow-up observations of the system mainly because of a remarkable triple transit that they observed with the HAWK-I instrument on the VLT. This transit showed clearly that at least one other unknown planet was orbiting the star. And that historic light curve shows for the first time three temperate Earth-sized planets, two of them in the habitable zone, passing in front of their star at the same time!
[4] This is one of the main methods that astronomers use to identify the presence of a planet around a star. They look at the light coming from the star to see if some of the light is blocked as the planet passes in front of its host star on the line of sight to Earth — it transits the star, as astronomers say. As the planet orbits around its star, we expect to see regular small dips in the light coming from the star as the planet moves in front of it.
[5] Such processes could include tidal heating, whereby the gravitational pull of TRAPPIST-1 causes the planet to repeatedly deform, leading to inner frictional forces and the generation of heat. This process drives the active volcanism on Jupiter’s moon Io. If TRAPPIST-1h has also retained a primordial hydrogen-rich atmosphere, the rate of heat loss could be very low.
[6] This discovery also represents the largest known chain of exoplanets orbiting in near-resonance with each other. The astronomers carefully measured how long it takes for each planet in the system to complete one orbit around TRAPPIST-1 — known as the revolution period — and then calculated the ratio of each planet’s period and that of its next more distant neighbour. The innermost six TRAPPIST-1 planets have period ratios with their neighbours that are very close to simple ratios, such as 5:3 or 3:2. This means that the planets most likely formed together further from their star, and have since moved inwards into their current configuration. If so, they could be low-density and volatile-rich worlds, suggesting an icy surface and/or an atmosphere.
** In this video, British science writer Philip Ball advocates a search for extraterrestrials based on the assumption that they share extremely little with humans in terms of biology, ways of thinking, etc (via Leonard David)
** Here is a Google talk by Paul Horowitz of Harvard about, “The Search for Extraterrestrial Intelligence“:
Paul Horowitz visited Google’s office in Cambridge, MA to discuss the SETI (Search for Extraterrestrial Intelligence) project at Harvard University.
Establishing an electromagnetic communications link across a thousand light-years presents unique technological challenges. In his talk, Prof. Horowitz visits some highlights of the science and technology of SETI — Do THEY exist? Is communication possible? What is the best way? Is this just completely insane? — and describes interesting searches his project and others have been doing.
Paul Horowitz is a Research Professor of Physics and of Electrical Engineering at Harvard, and is co-author of The Art of Electronics.
** The SETI Institute takes many approaches to the search for ET. Here is a talk by Eliot Gillium about looking for optical rather than radio signals from ET – A Novel Approach to OSETI:
The Search for Extraterrestrial Intelligence is a blind search across many dimensions—space and time being the most obvious. Every good SETI researcher does their very best to make the minimal reasonable assumptions, but time and resources are always limited, so various strategic optimizations have been adopted. A potentially more efficacious approach is to simply cover as much of the search space as possible. The SETI Institute has made this the starting point of their ambitious and groundbreaking idea to survey the entire night sky, all night, every night at optical wavelengths. This talk will further detail the motivation and planned operation of this new instrument, a panoptic eye for interstellar laser pulses.
.