Astronomers Hypothesize that Milky Way Might Be Teeming with Planets

Planets Common Around Stars in Milky Way Galaxy

This artist’s illustration gives an impression of how common planets are around the stars in the Milky Way. The planets, their orbits, and their host stars are all vastly magnified compared to their real separations. Credit: NASA/ESA/ES

In the past, astronomers had no evidence that there were planets orbiting other stars. Now, they estimate that the Milky Way might contain huge numbers of planets, with rocky, Earth-sized worlds outnumbering the rest.

Astronomers have been using a technique based on Einstein’s Theory of Relativity, which implies that massive objects bend the fabric of spacetime. Kailash Sahu of the Space Telescope Science Institute in Baltimore, Maryland, states that on average, every star has a planet and since there are 100 billion stars in our galaxy, there might be as many as 100 billion planets. Sahu co-authored a new study, which appeared in Nature on January 11th.

Kepler-35 System

The Kepler-35 System: An artist’s rendition of the Kepler-35 planetary system, in which a Saturn-size planet orbits a pair of stars. Credit: Lynette Cook /

An exoplanet will bend light as it passes in front of its parent star, causing a slight brightening of the star’s light. Microlensing has allowed astronomers to look at a lot more stars for exoplanets. Unlike other methods, microlensing can discover planets with different masses and distances from their star.

Sahu’s team looked at 30 different microlensing events and found extrasolar planets that caused three of them. Microlensing observations have been known to miss a percentage of planets, the researchers used statistical analysis to get the number of exoplanets in the galaxy.

Sahu says that about one-sixth of stars should have Jupiter-like planets, half likely have Neptune-sized planets, and two-thirds should have Earth-like planets.

Reference: “One or more bound planets per Milky Way star from microlensing observations” by A. Cassan, D. Kubas, J.-P. Beaulieu, M. Dominik, K. Horne, J. Greenhill, J. Wambsganss, J. Menzies, A. Williams, U. G. Jørgensen, A. Udalski, D. P. Bennett, M. D. Albrow, V. Batista, S. Brillant, J. A. R. Caldwell, A. Cole, Ch. Coutures, K. H. Cook, S. Dieters, D. Dominis Prester, J. Donatowicz, P. Fouqué, K. Hill, N. Kains, S. Kane, J.-B. Marquette, R. Martin, K. R. Pollard, K. C. Sahu, C. Vinter, D. Warren, B. Watson, M. Zub, T. Sumi, M. K. Szymański, M. Kubiak, R. Poleski, I. Soszynski, K. Ulaczyk, G. Pietrzyński and Ł. Wyrzykowski, 11 January 2012, Nature.
DOI: 10.1038/nature10684

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