MOSCOW (MIPT) — The discovery by Michel Mayor and Didier Queloz was momentous in that they made it very clear how exoplanets may be sought using what is known as the radial velocity method, says Alexander Rodin from the Moscow Institute of Physics and Technology. The physicist is available to comment on the recently awarded Nobel Prize in physics, as well as on planetary science and cosmology in general. Here are some thoughts he shared for a start:
“When astronomers say a planet is in orbit around a star, what they actually mean is that both the planet and the star are orbiting around their common center of mass. Sure, the motion of the star has a much smaller amplitude and speed, but as it turns out, it can still be measured. This underlies the radial velocity method for locating extrasolar planets.
“To detect a host star’s ‘wobble,’ astronomers exploit the so-called Doppler effect: The light emitted by a star predictably shifts depending on its velocity, periodically becoming redder or bluer. Sophisticated instruments can discern these slight variations and therefore detect changes in the star’s velocity as small as tens of meters per second.
“Such sensitivity enables the discovery of exoplanets. Naturally, this wobble is particularly noticeable when a planet is massive and its orbit lies close to the parent star. This explains why the first known exoplanet — 51 Pegasi b, discovered by Mayor and Queloz — is close to Jupiter in mass, while its orbital period is only slightly over four Earth days. It was the first in a class of similar exoplanets, and most of the ones discovered over the first several years were like it. This of course has nothing to do with their abundance, they are merely easier to find.
“Nowadays exoplanets are often discovered using another technique, called transit photometry. It involves registering the transit of a planet between the observer — us — and its host star, whose apparent brightness drops slightly, as the exoplanet eclipses some of the light. This approach sometimes even provides insights into the planet’s atmospheric composition. However, it is only applicable in those rare cases when both the planet and its star are directly in our line of sight. The method of Mayor and Queloz is more universal.
“I find it somewhat surprising that this year’s Nobel Prize in physics went to astronomers. While there is no separate prize in astronomy, it is worth noting that both cosmology and exoplanet science, which is obviously none other than observational astronomy, are disciplines distinct from physics.
“I think that from one point of view, this could point to physics losing its 20th-century claim to being the ‘paragon’ of all sciences. Then again, this could be seen as evidence of the triumph of physics. I mean, no scientific discipline today can exist without physics. In a way, everything’s become physics, astronomy included.”
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