Search for a world like our own

Kuldip Singh Dhir

In 1995, two astronomers discovered a planet circling a star other than our sun, changing our perception of the universe. Since then, hundreds of exoplanets have been discovered. This book is a cutting-edge story of the history and science of this search. It starts with Geoffrey Marcy and Paul Butler trying to detect planets around brown dwarfs. Meanwhile, Michel Mayer discovered one with the help of Queloz. They discovered 51 pegasi-b, the first exoplanet in 1995. Within weeks, Marcy and Butler found another giant planet around 47 Ursa Majoris. And so this narrative moves on introducing us to researchers, tools, instruments, principles, methods and achievements of search for exoplanets.

The roaster of exoplanets grew to seven within a year. Marcy and Mayer did a good job as planet hunters. Early scientists used radial velocity method for giant planets and transit observations for smaller ones. Gravitational lensing and direct imaging were the two other methods. Clark’s narrative brings out that large and very large telescopes, observatories, advanced missions, advances in spectroscopy, imaging and analysis techniques both on ground and in space changed things fast.

Nasa astronomer Borucki joined Marcy at the Lick observatory to track 6,000 stars. They proposed construction of the ambitious planet hunting mission, Kepler, in 1998. After dithering for three years, its construction began in 2002. Without wasting time, they started turning Keck telescope into a planet hunting machine. They drew up a list of about 1,000 stars and began a decade of extraordinary achievement. The name of the game was finding smaller and smaller planets now.

A significant development was installation of a very large telescope in Chile in 2001. Harps spectrometer and Spitzer Space Telescope started functioning in 2003. To detect small planets, Space Interferometry Mission was launched in 2005. These were salad days for planet hunters who were announcing new planets regularly. Some of these seemed rocky planets. In early 2006, an outlandish planet was detected near the galactic centre. It contained large underground lakes under deep layers of ice. In 2005, Marcy was awarded one million dollar Shaw Prize referred to as the Nobel Prize of astronomy. He and his team had discovered 110 planets.

Kepler, launched in 2009, can monitor thousands of stars, hundreds and thousands light years away. In early 2011, it presented its first rocky planet discovery around Keplar-10. Kepler team said that they were sitting on 1,100 planets, more than double the number of planets discovered in the last 16 years. The figures were from the first four months only. The rest of the data from 1,56,000 stars was yet to be analysed. Marcy emphasised the need to focus on nearby stars, which might be reachable eventually with next generation probes.

Narrowing the field further, astronomers decided to focus on Earth-sized habitable planets. They estimated that there were around 600 million habitable worlds in our Milky Way. Kepler announced 207 Earth-sized candidate exoplanets, out of which 48 might be in the habitable zone. Sara Seagar said in 2012 that Earth’s twin is sitting in Kepler’s data and we will find it out. In early 2012, Keplar developed a serious glitch. Meanwhile, it made spectacular detections around Kepler-11, Kepler-22 and Kepler-62. Scientists are increasingly confident now about discovery of an Earth’s twin in the next few years.

Scientists feel that exoplanet families are not similar to our solar system in form or architecture. Smaller planets near the star and bigger gaseous giants further away are not the necessary pattern. Real Earth twins seem rare. At present, it seems easier to locate our cousins. James Web Telescope, to be launched in 2018, would target red dwarfs. In February 2014, another advanced mission Plato was given green signal for launch in 2024. It will have a field of view 20 times larger than Kepler. If an Earth twin is there, Plato will find it out unless someone finds it earlier.

Clark concludes by telling that Espresso is the latest instrument for detecting small rocky planets. It has started operating on Chile’s VLT. Electronic eyes of the European Extremely Large Telescope will open to the universe in 2024, the year of scheduled launch of Plato. Clark’s narrative evinces not only his command over the bare facts in this fast changing area of science, but thorough knowledge of the science and the struggle of scientists concerned. An unputdownable book indeed.