31Dec2013

Closest Sun-Like Star May Have Planets

Tau Ceti recently crashed into the headlines after it was announced that a system of five worlds may be in orbit around the star.

An international team of scientists, including Carnegie’s Paul Butler, has discovered that Tau Ceti, one of the closest and most Sun-like stars, may have five planets.

Their work is published by Astronomy and Astrophysics and is available online. At a distance of twelve light years and visible with a naked eye in the evening sky, Tau Ceti is the closest single star with the same spectral classification as our Sun.

Its five planets are estimated to have masses between two and six times the mass of the Earth–making it the lowest-mass planetary system yet detected. One of the planets lies in the habitable zone of the star and has a mass around five times that of Earth, making it the smallest planet found to be orbiting in the habitable zone of a Sun-like star.

The international team of astronomers, led by Mikko Tuomi from the University of Hertfordshire, combined more than six-thousand observations from three different instruments and applied intensive modeling to the data.

Using new techniques, the team found a method to find signals half the size previously thought possible, which greatly improves the sensitivity of searches for small planets and suggests that Tau Ceti is not a lone star but has a planetary system.

Location of Tau Ceti in the constellation Cetus.

Location of Tau Ceti in the constellation Cetus. (Photo credit: Wikipedia)

“We pioneered new data modeling techniques by adding artificial signals to the data and testing our recovery of the signals with a variety of different approaches,” Tuomi said. “This significantly improved our noise modeling techniques and increased our sensitivity to find low mass planets.”

Tau Ceti was chosen for this noise-modeling study because the team thought it had no signals and would be a good benchmark system to test their methods for planet detection.

This is particularly true because it is so bright and similar to our own Sun. It’s also one of Earth’s nearest cosmic neighbors, so scientists could be able to learn about the atmospheres of these planets in the not-too-distant future.

More than 800 planets have been discovered orbiting other worlds, but planets in orbit the around the nearest Sun-like stars are particularly valuable for research.

“We are now glimpsing for the first time the secrets of our nearest companion stars and their previously hidden reservoirs of potentially habitable planets,” Butler said. “This work presages the time when we will be able to directly see these planets, and search them for water, carbon dioxide, methane, and other signposts of life.”

Within Reach?

Not only is Tau Ceti’s “super-Earth” a curious objective for astronomers to seek out extraterrestrial life, the nearby star could be within the reach of a future interstellar mission.

Tau Ceti may well be in our proverbial “cosmic backyard,” but it is still 12 light-years from Earth. The energies and speeds needed to make a hypothetical (unmanned) probe a reality aren’t possible using current technologies, but according to Paul Gilster, co-founder of the Tau Zero Foundation and author of the book Centauri Dreams (and writer for the blog of the same name), such a feat may not remain “impossible” for too long.

“Pushing a ‘lightsail’ by beamed laser or microwave propulsion (leaving the ‘fuel’ at home) may be able to get us up to ten percent or so of the speed of light, which would give us a mission to Tau Ceti of a bit over a century,” Gilster said.

“Fusion prospects of the kind studied by Project Icarus (one of the projects managed by the non-profit organization Icarus Interstellar) are also an option, though sails have already been demonstrated in space and are further along in their development.”

Artist impression of the Icarus starship accelerating past Jupiter, gaining a valuable boost in speed with the help of the gas giant’s gravity. Image courtesy Adrian Mann

There’s also the possibility of using antimatter to get “maximum bang for the buck,” Gilster points out, but we have yet to develop a means of generating enough antimatter for it to be used as an interstellar fuel. And then there’s the tricky matter (no pun intended) of storing the stuff and controlling the reactions inside a hypothetical antimatter engine.

But this is the reason why we should be researching multiple avenues of research when it comes to the possible modes of interstellar travel.

“The Tau Zero Foundation hopes to advance the human prospect for interstellar flight by defining the issues and keeping all the propulsion options on the table,” Gilster points out. “It is simply too early to down-select to a single propulsion system.

“Instead, incremental advances across the spectrum of possibilities will help us, over time, learn which methods will offer the soundest prospects. We’d like to encourage and, when it becomes possible, assist in the funding of such research.

“A second goal is to keep the idea of interstellar flight in front of the public through education, so that the relevant research is not only highlighted but supported through both philanthropy and government.”

Going Interstellar By Public Demand

The selection of propulsion methods is one thing, but interstellar advocates agree that when we do detect that bona fide habitable world — with hints of a biosphere and presence of liquid water — the public will demand further study.

And that means physically going there.

“In the event a habitable planet around a nearby star like Tau Ceti is confirmed, the best next step would be a space-based observatory specifically targeting nearby stars (Kepler’s targets are much more remote in order to take the statistical pulse of the planet population),” said Gilster. (Targeted searches have been carried out by SETI, in the hope of detecting a radio signal from a hypothetical alien civilization in the Tau Ceti system — but none have detected any artificial transmissions.)

http://www.icarusinterstellar.org/wp-content/files_mf/joebergeronbig.jpg

Daedalus by Joe Bergeron

“I have often imagined the day when scientists directly image an Earth-like extra-solar planet,” Icarus Deputy Project Leader Robert Freeland told Discovery News during an interview in October after the discovery of a small exoplanet orbiting Alpha Centauri (a binary star located only 4.4 light-years away). “We would be able to determine the planet’s atmosphere and surface temperature from its spectrum, and we would thus know whether it might be able to sustain life as we know it.

“I suspect that once such a discovery hits the news, people worldwide are going to demand that we send a probe to determine whether the planet has life (of any type) and/or could be suitable for human habitation,” Freeland added.

“Tau Ceti is about 12 light-years away, and with the right instrumentation, we will be able to make a spectroscopic analysis of the atmospheres of planets there,” Gilster said. “If we discover a biosignature indicating life is present, this will clearly make such a planet a priority for any future probes. A probe like this could get into space in the next two decades if funding emerges.” Source: Space Daily

 

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