1. No one else found more extrasolar planets than you and your colleague R. Paul Butlar, but the first extrasolar planet around a Sun-like star, 51 Pegasi, was discovered by another team (by Michel Mayor and Didier Queloz). Did that rankle you?
I was absolutely delighted about the discovery of 51 Pegasi. This opened a new field of science that all mankind would enjoy. What a wonderful time that was, when Michel and Didier discovered 51 Pegasi. It was the happiest time of my life. And our technique for measuring Doppler shifts was immediately useful. We confirmed the planet around 51 Pegasi within one week during October 1995.
Within two months we found the next two planets, orbiting 70 Virginis and 47 Ursae Majoris. 70 Virginis was in an elliptical orbit proving that it really was a planet and not an oscillation of the star. And 47 Ursae Majoris had an orbit larger than 1 Earth-Sun distance, making it a Jupiter-like planet that was similar to our own giant planets, Jupiter and Saturn. While 51 Peg was strange with its 4-day orbit, these two planet were definitively orbiting and connected to the planets we humans had known for thousands of years around our Sun.
2. For a long time, most scientists were not interested in the search for extrasolar planets, and many during the 1980s and 1990s believed that searching for distant worlds was a waste of time. Your decision to pursue these planets was risky, especially for your scientific career. Why did you take that risk?
I decided to search for planets in the 1980's because I dearly wanted to know if our Earth was unusual in the universe. I wanted to know if other habitable worlds were common or rare. And I wanted to know if life in the universe was common or rare. We are still attempting to answer those questions!
3. Which of the many worlds you've discovered do you find most interesting?
The most important discovery was the three planets orbiting Upsilon Andromedae. That was the first planetary system ever discovered.
And it was a triple planet system. The importance is that many people wonder if the exoplanets found up to that time were simply binary stars with a very small "companion". After all, 51 Peg had a tight orbit like some binary stars, and some of the exoplanets were in highly elliptical orbits similar to binary stars. Many scientists said that they would not believe these were exoplanets until someone discovered a multi-planet system. Upsilon Andromedae with its three planets provided the first example of a full family of planets such as we have orbiting the Sun.
4. The Holy Grail in the search for extrasolar planets is the discovery of a second Earth, when do you think will this happen?
Astronomers will discover the first Earth-like planets in the next three years. The Kepler mission is sure to find them, if they exist. We don't know, however, if Earths are common or rare.
5. NASA plans to return to the Moon and is scheduled in the late 2030s to fly to Mars. Do you think the Constellation program is a good idea?
NASA's idea to send people back to the Moon needs to be reconsidered. There are not many science questions that can be answered by going back to the moon. And young people will not be inspired if we go back to the Moon.
I strongly agree that a program to send humans to Mars will be scientifically very valuable, and inspirationally very exciting. Some day, we humans must colonize Mars and make living there possible. It is crucial that homo Sapiens spread its roots far enough to ensure our survival over the centuries and beyond.
6. The Miller-Urey experiment from the 1950’s shows that the building blocks of life are easier to create than previously thought and the Drake equation from the 1960’s predicts the number of extraterrestrials civilizations that we might come in contact with. Do you think that there could be intelligent lifeforms out there?
Our Milky Way Galaxy contains at least 200 billion stars, many of which are similar to our Earth. We now know that at least 20% of them harbor planets. Surely many of those planets are rocky, with hard surfaces and liquid water. I estimate that our Milky Way contains at least 20 billion rocky planets and about 1/3 of them have water on their surfaces, making them suitable for life as we know it. I have no doubt that primitive life is common in the Milky Way.
But intelligent life requires many more ingredients, such as stable continents and atmosphere. It also requires a stabilizing moon and a distant Jupiter that cleans the planetary system of its terrible comets and asteroids that would hit the home planet, destroying the advance life. Also, if intelligent life were common, they would have developed millions of years ago and we would know of their presence from their great energy use and their robotic spacecraft visiting us. As we don't see evidence of intelligent life yet, it probably is rare in our Galaxy. Perhaps there are only a few, and maybe only one, intelligent civilization in the Milky Way Galaxy.
Thank you very much for the interview.