Published on December 19th, 2012 | by Michael Ricciardi
Nearby Sun-like Star May Host Five Planets – One is Potentially Smallest Yet Found in a Habitable Zone [InfoGraphic]
The star is called Tau Ceti and it’s a mere 12 light years away from our own — practically in our solar system’s back yard.
Even more impressive, one of the five suspected planets that orbit Tau Ceti appears to be orbiting within the star’s habitable zone — an invisible zone around a star within which a planet could harbor liquid water on its surface.This is sometimes referred to as the ‘Goldilocks Zone’ as it amounts to a distance from a star (of a particular size and type) that is “just right” for liquid water, and possibly, even life, to exist.
What’s more, this planet has a minimum mass of just 4.3 Earth masses – making it (potentially) the smallest yet found in the habitable zone of a sun-like star.
New Data Analysis and Modeling Techniques
A team of astronomers and planetary scientists lead by Mikko Tuomi, of the University of Hertfordshire in England, found the tell-tale gravitational wobbles in the star’s movement (indicative of an orbiting planet) using a combination of techniques: one tried and true method, known as radial velocity, was combined with new data analysis and modeling techniques that added artificial signals to the data. Recovery of these signals was then attempted using a variety of different analysis methods.
The new techniques allowed the team to separate the weak, planetary signals from the usual (and continuous) noise due to stellar activity and other sources. This approach, says Tuomi, “significantly improved our noise modeling techniques and increased our ability to find low-mass planets.”
The new techniques should make planet hunting a bit easier — and further increase discoveries of small-mass exoplanets throughout our galactic neighborhood, and beyond.
A Combination of Planet Hunting Instruments
Prior to the team’s announcement of the newly discovered exoplanets, the team had to first re-analyze over 6000 observations made by three spectrograph instruments: the High Accuracy Radial velocity Planet Searcher (HARPS), on the European Southern Observatory’s 3.6-meter telescope in La Silla, Chile; the University College London Echelle Spectrograph (UCLES) on the Anglo-Australian Telescope in Siding Spring, Australia; and the High Resolution Echelle Spectrometer, or HIRES, on the 10-meter Keck telescope atop Mauna Kea in Hawaii.
More Info on the Exoplanets
The five detected planets are considered relatively small as their minimum masses range from 2 to 6.6 Earth masses. The potentially habitable world (Tau Ceti e makes a fairly fast solar cycle — orbiting its parent star once every 168 days. Despite its presence in its star’s habitable zone, researchers doubt it is a rocky planet.
In an interview with SPACE.com, Tuomi stated that “It is impossible to tell the composition, but I do not consider this particular planet to be very likely to have a rocky surface,It might be a ‘water world,’ but at the moment it’s anybody’s guess.”
As for the other, closest orbiting exoplanets, Tuomi stated:
“I am very confident that the three shortest periodicities (of 14, 35 and 94 days) are really there, but I cannot be that sure whether they are of planetary origin or some artifacts of insufficient noise modelling or stellar activity and/or magnetic cycles at this stage.” [quote source]
These innermost three have been designated Tau Ceti b, c, and d (moving from inner to outermost) as per convention, and all orbit closer to their parent star than Mars does to ours.
The most distant world (Tau Ceti f) detected around the star has a orbital period of 640 days.
Though the results are not official yet — they remain just discoveries until final confirmation (duplicate observations and analyses) — they offer yet more evidence to support the emerging view that nearly all stars have orbiting planets
In a press statement, co-author Steve Vogt, of the University of California, Santa Cruz, said: “This discovery is in keeping with our emerging view that virtually every star has planets, and that the galaxy must have many such potentially habitable Earth-sized planets. They are everywhere, even right next door.”
More About Tau Ceti
One might recognize the ‘Ceti’ in the star’s name as resembling the root in cetacea, which is the taxonomic designation for whales; Tau Ceti is in the constellation Cetus (The Whale). The star, visible to the unaided eye, is 11.9 light years distant (just about 70 trillion miles) and slightly smaller and less luminous that our sun (Tau Ceti puts out only 45% as much light as the sun).
Tau Ceti has been the target of at least one previous exoplanetary search (in 1960) but with negative findings. But now, aided by these new signal-adding/subtracting modelling techniques, scientists are able to “extract” very faint signals from a very noisy background, making this recent discovery of five planets possible.
If confirmed, the newest batch of exoplanets will be the second closest exoplanets; the closest being Alpha Centauri Bb at just 4.3 light years away, Alpha Centauri being our closest stellar neighbor.
Some source material for this post came from the Sci Am article ‘Potentially Habitable Planet Detected around Nearby Star’ by Mike Wall and SPACE.com
Check out this great exoplanet infographic courtesy of SPACE.com:
Top Image: (Artist’s impression of five possible planets orbiting the star Tau Ceti, which is just 11.9 light-years from Earth) J. Pinfield for the RoPACS network at the University of Hertfordshire, 2012.
45% as much light as the sun,