Artists conception of Kepler-62f, an exoplanet that could support life. (Image: NASA/Ames/JPL-Caltech)

An astronomer born 100 years ago is coming into his own.

This week, we celebrated the 100th birthday of Wilhelm Gliese — pronounced “Gleesa” — an obscure German astronomer. Over the next few years, Gliese is going to become a household name.

Ceres, the dwarf planet that lives in the asteroid belt between Mars and Jupiter, is being photographed up close for the first time; those photos are giving everyone a taste of the excitement of Voyagers 1 and 2 sending back the first-ever close-ups of the gas giants. The Dawn satellite’s photos of Ceres’s mysterious shining white spots and a lonely, Matterhorn-sized mountain are whetting everyone’s appetite for the first-ever close-ups of Pluto — which should arrive on Earth soon after NASA’s New Horizons spaceship arrives at our erstwhile ninth planet, in two weeks and three days.


When New Horizons reaches Pluto, it won’t stop; it’s going much too fast. Carrying enough fuel to slow it into a Pluto-centric orbit would have added lots of weight and years of travel time; instead, it will zoom past, snapping photos as it goes. Pluto is the second-largest of five confirmed dwarf planets in the Kuiper belt, an asteroid belt beyond Neptune. New Horizons won’t make it to any of the other Kuiper dwarves, but once Pluto is passed, chances are good that the New Horizons team will find another large and interesting Kuiper object to point their spaceship toward. Something else that will help shed some light on the dim and distant trans-Neptunian solar system.

So what’s after the Kuiper belt? Technically, the Oort cloud — a spherical scattering of icy proto-planets and dust. Unfortunately, since it’s a thousand times further away from the sun than Pluto and the Kuiper belt are, it’s too far to visit and too far from a light source to see. Instead, once we get our first good glimpse of Pluto, the next big deal in planetary science will be getting a good look at some exoplanets.

Exoplanets are planets outside our solar system. So far, 1,932 have been discovered. The smallest is smaller than Mercury; the largest is 29 times more massive than Jupiter. Most of the exoplanets are either Neptune-sized or “super-Earths,” which are between one and a quarter and two times Earth’s mass. A super-Earth named GJ 1214 b is believed to be made entirely out of water: a water mantle over a water core. Another, named PSR J1719-1438 b, is believed to be made entirely out of crystal diamond. A member of a Jupiter class of planets that orbit very close to their stars — “hot Jupiters” — is nearly as black as a thing can be; it absorbs more than 99 percent of the light that hits it. There’s a hot Neptune whose average surface temperature is 800 degrees Fahrenheit — even though its entire surface is made out of ice. It orbits so close to its host star that gravity squeezes what should be steam into an absurd, exotic ice crust. Its name is Gliese 436 b.

As interesting as planets made of boiling ice or diamond are, nothing trumps dreams of paradisiacal alien Edens.

As I said, Wilhelm Gliese isn’t an especially well-known astronomer. However, he was the first to catalogue and study a plethora of stars that turned out to host exoplanets — all of which have adopted his surname. Among Gliese’s exoplanets are seven believed to orbit a triple-star system called Gliese 667. Of those seven planets, three are believed to orbit inside the “habitable zone,” the range of a star system where it’s neither too hot nor too cold for liquid water. One planet in the habitable zone, Gliese 677 Cc, is remarkably similar to Earth: about Earth’s mass, about Earth’s temperature, and with the potential for an Earth-like atmosphere. It’s at the top of the list of planets where we might find life. And as interesting as planets made of boiling ice or diamond are, nothing trumps dreams of paradisiacal alien Edens.


The trick will be getting a look at them. They’re all far too far away to visit. New Horizons is the fastest spaceship we’ve ever launched; at its top speed of 51,000 miles per hour, it would take 195,000 years to reach the nearest confirmed exoplanet. (Which is Gliese 674 b.)


So we’ll have to figure out how to photograph them from here. As you’ve noticed, the further you are from a light source, the dimmer it appears. Specifically: Brightness diminishes in inverse proportion to the square of distance — when you’re twice as far away, you get a quarter of the light; three times as far, one-ninth the light, and so on. To take a photograph of something, you’ve got to gather enough of the light that bounced off it, enough light-pixels, to assemble an image. The dimmer the source, the longer that takes; to take a photograph of something as far and dim as an exoplanet, you’ve got to keep your camera pointed at it for a very long time. Unfortunately, planets move; they orbit and they rotate, and that’s going to blur your photos.


And to get even a blurry photo of an exoplanet, you’d need a much, much bigger telescope than anything we have now (needless to say, the bigger — the wider — the telescope, the more light it collects). But don’t worry, we’ll work it out. And before too long.


Wilhelm Gliese’s 100th birthday was this past Sunday. Of the 30 most Earth-like planets, seven share his name. As we enter the next stage of planetary science, he’s going to become a retroactive bigshot. What a time to be alive.

— Josh Gelernter writes weekly for NRO and is a regular contributor to The Weekly Standard.