Woot! 4,001 exoplanets and counting 

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This week – March 12, 2019 – an international group of astronomers is celebrating humanity’s discovery of the 4,001st exoplanet, or planet orbiting a distant star. The Exoplanet Team, led by the Observatoire de Paris, maintains a list of exoplanets online at website called The Extrasolar Planets Encyclopaedia. On March 12, the site ran this announcement:

Today is a celebration day as we are now over 4,000 planets validated in our database, and this number will grow very quickly thanks to intensive ongoing work!

The discovery of two new exoplanets brought the tally to the 4,000 mark. The newly found planets both orbit around the multiple star system labeled EPIC 203868608, at a distance of 499 light-years from Earth, in the direction of the constellation Scorpius the Scorpion.

Astronomers Alex Wolszczan and Dale Frail discovered the first two known exoplanets, and then a third one, in 1990 from the Arecibo Observatory. Those pulsar planets orbited around pulsar PSR B1257+12, the remnant of a massive star.

Then, in 1995, scientists found a planet around 51 Pegasi, the first planet detected around a main-sequence star, or star in the same stage of its evolution as our sun.

Since then – through various means both ground-based and space-based – astronomers have confirmed thousands of other exoplanets, with an incredible diversity of orbits, including some planets in multiple systems. Those worlds have two or even three suns in their skies.

Abel Mendez, director of the Planetary Habitability Laboratory (PHL), of the University of Puerto Rico at Arecibo, told EarthSky:

At least 49 of the known exoplanets are potentially habitable.

For exoplanets – as for Earth – conditions for habitability might need to include a stable orbit around a star and a distance from the star that’s not too close and not too far. Those conditions are needed for a planet to sustain liquid water on its surface. Can life exist on a planet without liquid water on its surface? We don’t know.

Although there are 4,001 known extrasolar planets as of March 12, 2019, many new ones are likely to be discovered very soon. NASA’s new Transiting Exoplanet Survey Satellite (TESS) mission is analyzing up to 85 percent of the sky. That’s about 350 times more area than the limited sky zone observed by the Kepler Space Telescope, which has detected the lion’s share of exoplanets so far, more than 2,700 exoplanets.

This video, by the way, shows all of the Kepler multi-planet systems (1815 planets/planet candidates in 726 systems) from Kepler’s original mission as of the announcement of Kepler’s end of life on October 30, 2018. The systems are shown together at the same scale as our own solar system (dashed lines). The video is via Ethan Kruse, and is based on Kepler (NASA/JPL-Caltech) data.

Theoretically, astronomers say, our Milky Way galaxy might contain billions of exoplanets. We now know that even the closest stars to our sun – including Proxima Centauri, at 4.3 light-years, and Barnard’s Star, located at just 5.98 light-years away – are orbited by planets.

We have just begun to discover these other worlds. Here’s to the next 4,000!

In the meantime, check out the video below, an artist’s concept showing the temperate planet Ross 128 b along with its red dwarf parent star. This planet, which lies only 11 light-years from Earth, was found by a team using the European Southern Observatory’s planet-hunting HARPS instrument.

Bottom line: As of March 12, 2019, astronomers know of 4,001 exoplanets!