Hunt for earth-like planets hots up
K.S. RAJGOPAL
— photo: AP
Stupendous task: The Kepler space telescope will survey more than 100,000 stars in our galaxy.
The launch of NASA’s Kepler telescope is targeted for no earlier than tomorrow (6th March), at Cape Canaveral Air Force Station in Florida. Kepler is a spaceborne telescope designed to search the nearby region of our galaxy for Earth-size planets orbiting in the habitable zone of stars like our sun.
The habitable zone is the region around a star where temperatures permit water to be in a liquid state on a planet’s surface.
Liquid water is considered essential for the existence of life as we know it. The vast majority of the approximately 300 planets known to orbit other stars are much larger than Earth, and none is believed to be habitable.
The challenge
The challenge for Kepler is to look at a large number of stars in order to statistically estimate the total number of Earth-size planets orbiting sun-like stars in the habitable zone. Kepler will survey more than 100,000 stars in our galaxy.
Mr. J.D. Harrington, Public Affairs Officer, NASA, explaining how the nearby region would be surveyed by the telescope, noted in an email to this correspondent: “Kepler will stare continuously at a large field of view. Kepler will be looking along the Orion spiral arm of our galaxy. The distance to most of the stars in this field for which Earth-size planets can be detected is between 600 and 3,000 light years.
“The field of view was chosen so there would be a large number of stars in the brightness range where an Earth-size transit is detectable.”
Kepler observations will result in measuring the distance of the planet from its star. This in turn would help in inferring the approximate surface temperature of planets, if the star’s properties are well known.
The tricky part is that, while Kepler surveys more than 1,00,000 stars, there should be no repeated observations.
According to Mr. Harrington, though there are there are millions of stars in the Kepler’s field of view, a subset of stars that are most like the Sun has been carefully chosen to monitor for Earth-size transits.
The 100,000-odd stars will be observed simultaneously and virtually continuously by Kepler. The data from each of these stars will be analyzed for evidence of transits. “So, repetition is not a concern,” he noted.
Slight dimming
The Kepler spacecraft will look for Earth-sized planets moving around stars similar to the sun for about three-and-half years.
Kepler will look for slight dimming in the stars as planets pass between the star and Kepler using special detectors similar to those used in digital cameras. “Larger planets create more dimming and Kepler will find these too. However, the most interest is in Earth-size transits,” he explained.
For an Earth-size planet transiting a solar-like star, the change in brightness is only 84 parts per million. Kepler is designed to accurately measure such a change with high precision.
The Kepler’s place in space will allow it to watch the same stars constantly throughout its mission, something observatories like Hubble cannot do.
Orbital period
For planet to be called as earth-like, the orbital period should be the same as that of the earth. Earth transits the Sun 1 day out of the 365 days with respect to Kepler’s position. The same should hold true in the case of earth-like planets. Hence the same stars must be looked at constantly so that a transit (passage of the planet across the face of its parent star with respect to Kepler) is not missed.
The presence of an earth-like planet is confirmed only when at least three transits are observed.
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