51 Pegasi b is a planet originally and informally named “Bellerophon” after a Greek mythological hero who captured the winged-steed Pegasus for whom the constellation where 51 Pegasi is located is named.1 However, and since then, the International Astronomical Union has renamed the planet as Dimidium, which means “half.” The reference here is that Dimidium is half the mass of our planet Jupiter (though the planet, itself, is larger than Jupiter.) This suggests that the superheated atmosphere is not nearly as dense as Jupiter’s. Dimidium was discovered in October 1995. The temperature of the planet is roughly calculated to be 1,817 degrees F, and the planet, itself, is classified as a “Hot Jupiter.” Traces of water were detected most likely above the planet in 2017.
The discovery of 51 Pegasi b according to the Nobel Prize citation to the award presented to Dimidium’s discoverers notes that this planet was the first exoplanet found.
In October 1995, Michel Mayor and Didier Queloz announced the first discovery of a planet outside our solar system, an exoplanet, orbiting a solar-type star in our home galaxy, the Milky Way. At the Haute-Provence Observatory in southern France, using custom-made instruments, they were able to see planet 51 Pegasi b, a gaseous ball comparable with the solar system’s biggest gas giant, Jupiter.
This discovery started a revolution in astronomy and over 4,000 exoplanets have since been found in the Milky Way. Strange new worlds are still being discovered, with an incredible wealth of sizes, forms and orbits. They challenge our preconceived ideas about planetary systems and are forcing scientists to revise their theories of the physical processes behind the origins of planets. With numerous projects planned to start searching for exoplanets, we may eventually find an answer to the eternal question of whether other life is out there.
This year’s Laureates have transformed our ideas about the cosmos. While James Peebles’ theoretical discoveries contributed to our understanding of how the universe evolved after the Big Bang, Michel Mayor and Didier Queloz explored our cosmic neighborhoods on the hunt for unknown planets. Their discoveries have forever changed our conceptions of the world.
Dimidium. Not as idyllic as the feature photo suggests. Illustration credit: NASA, JPL-Caltech.
If you search Google for the first exoplanet found, you’ll find several different other planets identified, some with circumstantial evidence going back a century. These other planets all circled pulsars, however. But according to NASA, 51 Pegasus b is not only the first planet discovered, but it is different than all the other first place “also rans” because it orbits a Sol-like planet like ours, though it is so close to its star that life could not exist as we know it (the orbital period is only 4.4 Earth-days, which equates to 300,000 miles per hour.) This is only possible because Dimidium is a mere 4.97 million miles from its star (our own Mercury is ten times that distance from our sun.) DImidium is also tidally-locked, which means the same side of the planet always faces 51 Pegasus (like our moon always presents the same side to us.)
A volcanic landscape where fire salamanders forge paths of lava with their passage. A real stretch in so many ways, especially since 51 Pegasi b does not have a surface. Credit: AI Farm.
Could life exist on Dimidium? Certainly not life as we know it. But perhaps the dense layers of clouds contain the ingredients of life at least at the microbial level? Or, maybe life under those circumstances (e.g., without a firm surface on which to emerge, and in spite of those extreme temperatures and the chemistry of the atmosphere), some sort of “floating” life might exist, or something impervious to heat, much as the mythological salamanders were believed to be. But for now and what we know of Dimidium, and life in general, this seems very, very doubtful.
51 Pegasi is larger than our sun by a quarter and more massive as well. The star is approximately 50.91 light years from year, making a visit to that start system very unlikely for many centuries to come. And even at the speed of light, without a wormhole or suspended animation or cryogenic sleep, it would take a cosmonaut the better part of a lifetime just getting there.
Footnotes
1To say that a star is in a certain constellation does not mean that the star is in close proximity to other stars in the same constellation, but rather, from our vantage point on Earth, the star appears as part of whatever design the ancients ascribed to a particular field of stars (such as a “dipper,” a “cross,” a “bull” and so on.)
