New planets found around Sun-like stars

An international team of planet hunters has today announced the discovery of four new planets orbiting nearby stars like our Sun. The discoveries include both a mysterious new class of planet that is more massive than the Earth, but less massive than Uranus and Neptune, and a gas-giant planet that has a long-period orbit like that of Jupiter and could likely reside in a solar system reminiscent of our own, with the potential for life.

These new discoveries were made by British, Australian and American astronomers using the Anglo-Australian Telescope in New South Wales, Australia and the Keck Telescope in Hawaii. UK involvement comes from Hertfordshire University and is funded by the Science and Technology Facilities Council (STFC).

The long-period planet orbiting the star 23 Lib has an orbit similar to that of Jupiter which indicates that we now have the ability to detect the signatures of solar systems reminiscent of our own.

“Since Jupiter dominates the signal from our Solar System, we are now in a position to quantify how common planets like Jupiter are around stars like our Sun,” says Hugh Jones of University of Hertfordshire. “Compared to the Solar System, most extrasolar systems look odd, with planets in very small or very elliptical orbits. In contrast, this new planet has an orbit that is both large, and nearly circular - for the first time we are beginning to see systems that resemble our own.”

The Jupiter-mass planet orbits the star 23 Lib in a fourteen-year period, similar to Jupiter’s twelve-year orbit. The detection of long-period planets like this one is important. Of the planets in the Solar System, only Jupiter could be detected by current techniques. So finding a planet with an orbit like Jupiter’s suggests that astronomers are zeroing in on extrasolar planetary systems like our own.

The team also found some remarkable planets with much shorter orbital periods. “The sub-Neptune-mass planets we have found are very exciting”, said Chris Tinney of the University of New South Wales. “They suggest that a large number of nearby stars may harbour detectible planets with Neptune's mass or less. These small planets point the way to detecting potentially habitable worlds in the near future."

Three new planets with masses ranging from 5.3 up to 24.9 times the mass of the Earth have been found to orbit the star 61 Virginis, which at this time of year can be seen with the naked eye in the South East, in the constellation of Virgo rising in the morning ahead of the Sun. 61 Vir has long stood out amongst the hundreds of nearest stellar neighbours as being most similar to the Sun.

On one hand the 61 Vir and 23 Lib detections confirm our expectation that nearby stars like the Sun have planets like Jupiter and have multiple planets orbiting with periods less than an Earth-year. On the other hand, 61 Vir adds to a recent slew of discoveries that have upended conventional thinking regarding planet detection. “Our simulations suggest that more than a quarter of nearby stars have sub-Neptune mass planets in orbits shorter than a few weeks, in other words much closer to their stars than Mercury is to our Sun” said Simon O’Toole of the Anglo-Australian Observatory.

Notes for editors

Images and video

Graphic of the 23 Lib system (PDF - link opens in a new window)  

Caption: A comparison of the orbits of the planets of 23 Lib with our Solar System. Although 23 Lib c is likely to be similar to Jupiter, the inner planet 23 Lib b is a gas giant in a somewhat elliptical orbit smaller than that of the Earth.

Graphic of the 61 Vir system (PDF - link opens in a new window)  

Caption: A comparison of the orbits of the planets of 61 Vir with the inner planets in our Solar System. All three planets discovered to date in this system would lie inside the orbit of Venus.

Animation of 61 Vir b (link opens in a new window)  

Animation Caption: The animation shows a simulation of the hot atmosphere of the 5.3 Earth-mass planet 61 Vir b as it circles around its star in a 4.2 day orbit. The imaginary observer sits in space above the planet, and sees the hot side (which always faces the star) rotate into and out of view.

Collaboration

Both sets of planets were discovered through collaboration between the Anglo-Australian Telescope and the Keck Telescope. “These detections are truly at the current state-of-the-art,” said team member Paul Butler of the Carnegie Institute of Washington, “The inner planet of the 61 Vir system is among the two or three lowest-amplitude planetary signals that have been identified with confidence. We’ve found there’s a tremendous advantage to be gained from combining data from two world-class observatories, and it’s clear that we’ll have an excellent shot at identifying potentially habitable planets around the very nearest stars within just a few years.”

The 61 Vir System

Data from the Anglo-Australian and Keck Telescopes was used in combination to reveal the presence of three planets orbiting the “solar twin” 61 Vir – so-called because amongst our hundreds of nearest stellar neighbours, it stands out as being the most nearly similar to the Sun in terms of age, mass, and other essential properties.

Recently, a separate team of astronomers used the Spitzer Space telescope to discover that 61 Vir also contains a thick ring of dust at a distance roughly twice as far from 61 Vir as Pluto is from our Sun. This dust is apparently created by collisions of comet-like bodies in the cold outer reaches of the system. According to team member Dr. Eugenio Rivera, “Spitzer’s detection of cold dust orbiting 61 Vir indicates that there’s a real kinship between the Sun and 61 Vir.” Rivera computed an extensive set of numerical simulations that show that a habitable Earth-like world could easily exist in the as-yet unprobed region between the newly discovered planets and the outer dust disk.

These results for 61 Vir (PDF - link opens in a new window)are to be published in The Astrophysical Journal

The discovery of the Jupiter-like planet orbiting 23 Lib is also a collaboration between the Anglo-Australian Telescope and the Keck Telescope, both of which have been following this star for more than a decade. They previously reported a giant planet orbiting 23 Lib (known as 23 Lib b) in an elliptical 8 month orbit. “This makes this yet another unexpected oddball – a system with a circular Jupiter-like planet, but with an interior planet in an eccentric orbit,” notes Rob Wittenmyer of the University of New South Wales.

These results for 23 Lib (PDF - link opens in a new window)have been submitted for publication in The Monthly Notices of the Royal Astronomical Society.

Links

Anglo-Australian Planet Search (link opens in a new window) –

Anglo-Australian Observatory (link opens in a new window)

The Lick-Carnegie planet search team has developed a publicly available tool, the Systemic Console (link opens in a new window) which enables members of the public to explore real data sets in a straightforward and intuitive way.

Contacts

• Hugh Jones
  University of Hertfordshire, UK
  Tel 01727 861115
  Mob 07956 945276
  
  
• Julia Short
  STFC Press Office
  Tel: +44 (0)1793 442012
  
  
• Chris Tinney
  University of New South Wales, Australia
  Tel +61 2 93855168
  
  
• Paul Butler
  Carnegie Institution of Washington, USA
  Tel +61 2 9372 4800
  
  
• Steve Vogt
  UCO/Lick Observatory, USA
  Tel +1 831-459-2151
  
  
• Greg Laughlin
  University of California at Santa Cruz, USA
  Tel +1 831 459 3208
  
  

About STFC