How Many Planets?

ESO's 3.6 meter telescope

ESO's 3.6 meter telescope. Credit: ESO/H.H.Heyer

Apr 04, 2012

A European Southern Observatory study claims there are billions of rocky planets in the Milky Way.

Human beings have wondered about other planets for centuries. “Are we alone?” is probably one of the earliest questions after “where do we come from?” According to a recent publication from the European Southern Observatory (ESO), there could be planets galore in our galaxy alone, creating the possibility that humans are not its only sentient inhabitants.

The High Accuracy Radial Velocity Planetary Searcher (HARPS) is the most sensitive spectrograph ever built. Called “the planet hunter,” HARPS is able to formulate stellar spectrograms of unprecedented accuracy. This means that tiny Doppler shifts in starlight can be detected, making exoplanet hunting easier.

In the past, attempts to locate planetary bodies in orbit around distant stars suffered from the glare problem: stars are so bright that direct observation of a dim companion is impossible. A little over 16 years ago, astronomer Geoff Marcy announced the discovery of two exoplanets, 47 Ursae Majoris b and 70 Virginis b, both of which were found by analyzing the motion of their primaries.

As planets revolve, they pull on their parent stars. The stars “wobble” slightly, altering their spectrographic signatures. Astronomers knew that Doppler shifts could be used to identify binary stars—extremely massive objects—so it was thought that less massive objects could also be identified using that method. The difficulty with the procedure was that even large planets pull on stars by only several meters per second. What was needed was a more detailed picture of stellar spectra, or another way of conducting the search.

NASA launched the Kepler Space Telescope on March 7, 2009 on a three and a half year mission to search for Earth-sized planets around other stars. As of this writing, it has found 2321 planet candidates, with 61 confirmed. Kepler does not use Doppler shift as its means of detection, however. It uses a photometer to measure the reduction in light output as an object passes in front of a subject star. Kepler can scan 150,000 stars simultaneously utilizing that method. It does not do a good job with dim stars like red dwarfs, though.

The HARPS instrument is the solution to that difficulty. Since it can resolve the Doppler shifts of red dwarf stars, its analysis of 102 different red dwarfs over the last six years revealed nine so-called “super-Earths” (planets 1-10 times the mass of Earth) in the data. Two of them are in the “habitable zones” of their respective hosts. The habitable zone is the range of temperature in which liquid water can exist.

Based on that discovery, ESO scientists estimate that there are “tens of billions” of rocky planets in our galaxy, since red dwarfs are considered the most common star. There are said to be hundreds of red dwarf stars within 40 light years of Earth, so there could also be hundreds of super-Earth planets.

Since many exoplanets are larger than Jupiter, with orbits closer than Mercury is to the Sun, an argument for their creation in stellar electrical expulsion can be made. As Electric Universe advocate Wal Thornhill states: “How else should we expect to find an extrasolar planet whipping around its parent in a few days or in an eccentric orbit? Eccentric orbits should be short-lived. They hint at recent events in those distant planetary systems; perhaps the birth of a new planet.”

Also, as has been presented in previous Picture of the Day articles, rocky bodies, like Mercury or the Moon, are ejected from larger, highly charged objects. Whether they are red or brown dwarf stars, or gas giant planets, planets are not born in dusty eddies surrounding a stellar “cocoon”.

Instead, as Wal Thornhill proposes: “We observe stellar explosions to be highly directional, often forming bipolar cones or even collimated jets. Plasma physicists are well aware that powerful electric discharges form thin jets, often with condensations/knots of matter along them. And a collimated jet is a prime requirement for the birth of a planet from a star. Significantly, the light curve from stellar explosions is the same as that of lightning. There is a more simple and efficient process that fits the latest discoveries. It requires the expulsion, or ‘birth’ of a fully formed proto-planet from the core of a star or gas giant.”

Stephen Smith

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