Changing Planet

Far-Flung Exoplanet Puzzles Astronomers

Artist’s view of the planet GU Psc b (at right) and its distant star GU Psc (at left). Courtesy of Lucas Granito

Talk about a cosmic outsider! A newfound exoplanet sets the record for orbital distance from a host star.

Dubbed GU Psc b, the giant planet is on an orbit more than 2,000 times farther away from its star than the one the Earth circles around the sun. You wouldn’t see many birthdays on this exotic world, since it takes about 80,000 years to make a single trip around its star!

For comparison, the farthest large planet in our solar system, Neptune, orbits at only 30 times the Earth-sun distance. Its “year” is just shy of 165 Earth-years.

The newly discovered exoplanet lies some 155 light-years from Earth in the constellation Pisces, and it is huge, estimated at about 11 times the mass of Jupiter.

Current theories, however, cannot explain how a large planet like GU Psc b could form at such a great distance from its star, so the discovery may refine our understanding of how planets are born.

The international discovery team, led by Marie-Ève Naud of the Université de Montréal in Quebec, found and directly imaged the planet by combining observations from observatories in Canada, Hawaii, and Chile. The announcement made this week, published in the Astrophysical Journal, comes hot on the heels of the release of the best direct image ever taken of an exoplanet.


The planet GU Psc b and its star GU Psc composed of visible and infrared images from the Gemini South telescope and an infrared image from the CFHT. Credit: Gemini Observatory
The planet GU Psc b and its star GU Psc A are shown in a composite picture of visible and infrared images from the Gemini South telescope and an infrared image from the Canana-France-Hawaii Telescope. Credit: Gemini Observatory

See for Yourself

While GU Psc b is an extremely faint 14th-magnitude star, visible only through the largest of backyard telescopes, we can look at a much brighter and closer analogue—the giant Neptune. Neptune is the most distant planet in our solar system, leaving aside comet-belt dwarf planets such as Pluto and Eris.

Over the next few weeks Neptune will be some 2.8 billion miles (4.5 billion kilometers) away from Earth—so distant that reflected sunlight off its icy cloud tops takes nearly four hours to reach us. At this distance the planet’s 33,000-mile (53,000-kilometer) diameter is reduced to a mere 2.3 arc-seconds wide (compared to much closer and bigger Jupiter’s 40 arc-seconds), but it still shines at 7.9 magnitude—making it invisible to the naked eye but an easy target for binoculars.

The key in finding this denizen of the outer solar system is to know when and where to look.

It’s quite easy to find the general vicinity of Neptune, which lies among the starry background of the southern constellation Aquarius. The hard part is pinpointing which of those tiny points of light is the actual planet.

The planet rises above the eastern horizon after 3 a.m. local time and climbs higher until dawn in the Northern Hemisphere. For those with detailed star charts and GoTo scopes, its coordinate is RA 22h 37.2m, Dec -9º 28.9′.

Skychart showing hte southeast sky  about an hour before local dawn in the Northern Hemisphere. Neptune lies inear the border of the constellation Aquarius. Credit: SkySafari
This sky chart shows the southeastern sky about an hour before local dawn in the Northern Hemisphere. Neptune lies near the border of the constellation Aquarius. Credit: SkySafari

Start your hunt with a visible star low in the sky in Capricornus called Deneb Algiedi. Draw an imaginary line toward the left until hitting the next faintly visible star, Hydor (Lambda Aquarii) in Aquarius. Neptune is about one-quarter of the way from Hydor to Deneb Algiedi. The separation between Hydor and the planet is approximately 4 degrees, slightly less than the width of your three fingers at an outstretched arm’s length.

I recommend first trying to spot Neptune with binoculars, using the above sky chart for reference.

The best way to confirm your sighting is through a telescope. Center the object in the field of view and insert a high-power eyepiece. If the object appears as a small blue-gray disk and not a point of light, then you’ve bagged Neptune!

While there isn’t much Neptunian detail even through a large telescope, the real satisfaction comes from knowing you are actually watching the most distant major planet in the solar system with your own eyes.

Follow Andrew Fazekas, the Night Sky Guy, on TwitterFacebook, and his website.

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.
  • Dwayne LaGrou

    With the newly found planet being so huge I wonder if it could possibly be a failed star instead of an actual planet?!
    Anyone else think this might be that?

  • Craig Miller

    Dwayne, its all stardust. At one point the Earth was probably part of a star. In order to be a star the object must be at a certain size, maybe 16 Jupiter-masses. Although, my theory is that Jupiter sized planets or larger could have potentially been a failed star. Maybe objects smaller than 16 Jupiter-masses have enough gravity to combine certain elements to form other elements. And maybe an object of 16 J-masses began nuclear fission process, but never could become a star because it fell below the mass threshold to fully become a star.

  • paul

    Yep, that is what it is.

  • Raudo Cruz

    What a difference a day make !!!

  • Rune Olwen

    Yes, and whether the “orbit” is acutally one.
    Or is it more of a spiral (not one of moving away from its star centimeters per anno but soon independent).
    Three or four of those born with each visible star and independent after a few million earth years could explain some of the “dark matter”

  • pranav

    Just for fun, i did some math and.. well.. at the speed of light, it will take us 165 years to reach this place.. damn man.. thats a long time..

    Warp is not enough .. we need to go faster..

    wait a sec, we are just at 11 kmps (or whatever the record is ) as of now.. Damn damn damn.. keep taking pictures and be happy 🙁 🙁 ..

  • Shaun Gibson

    I don’t find it that puzzling. Even within current planet formation theory a couple of likely candidate pop up as explanations.

    a) It’s a failed star (we’re not THAT far off it being a brown dwarf)

    b) It formed closer and moved further out. Which we already know happened in our solar system.

  • 曾森

    It is a fasinating thing,I love astronomy!

  • Gianfranco Fronzi

    The relation of it’s mass in comparison to the star it supposedly orbits is some good gravitational information .
    On more information on mass of planet to stars mass . ” Fronzi Approved “.

  • Diego

    Favor en español,

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