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Artist's conception of what the planet may look like. Credit: NASA/JPL-CALTECH

Astronomers find closest confirmed rocky planet to Earth

The discovery of Kepler 452b, dubbed ‘Earth 2.0’ last week caused a lot of excitement on the Internet. But there have been several other exoplanets confirmed in the past few months. One of these is HD 219134b. What makes this find exciting is that it is the closet rocky planet to Earth found.

At a distance of just 21 light-years from Earth, the star it orbits, HD 219134, is visible to the naked eye. It is located in the constellation Cassiopeia. It is a K-dwarf star so, compared to the sun, it is fairly small but because it’s so close to Earth it is visible.

The planet is about 1.6 times the size of Earth and 4.5 times its mass. Using these measurements, the team estimates the density of the planet is about 3.5 ounces per square inch, which confirms the planet is terrestrial.

Unfortunately HD 219134b is not habitable. It completes its orbit around its star in just 3 days, which tells us it is much too hot on this planet to be habitable. In addition, at this distance, the planet would be tidally locked meaning one side would be in constant sunlight while the other would be in complete darkness.

But this is not why the discovery is significant. Although the planet wasn’t discovered using the transit method, it is in transit around its star. The transit method involves detecting tiny decreasing in the brightness of a star as the planet passes between us on Earth and the star. Planets detected using the transit technique are especially significant. This is because we can examine its atmosphere as it passes in front of its star.

What a transit looks like up close. The planet as it passes in front of the star causes a decrease in brightness. Credit: NASA/JPL-CALTECH
What a transit looks like up close. The planet as it passes in front of the star causes a decrease in brightness. Credit: NASA/JPL-CALTECH

What a transit looks like up close. The planet as it passes in front of the star causes a decrease in brightness. Credit: NASA/JPL-CALTECH

Its close proximity to Earth is also a game changer. This makes observations of the planet much easier. Ati Motalebi of the Geneva Observatory thinks this planet would be a good candidate for the James Webb telescope, the successor to the Hubble Telescope.

“Transiting exoplanets are worth their weight in gold because they can be extensively characterized. This exoplanet will be one of the most studied for decades to come.” said Michael Werner, project manager of the Spitzer Telescope.

This planet will be studied in great detail in the coming years.

It was discovered using the radial velocity technique. A planets mass can actually cause its star to move as it orbits. These small shifts in the location of the star can be detected and the presence of a planet can be inferred. The planet was confirmed by the Spitzer space telescope, which revealed it was transiting its star relative to the Earth.

What’s more, this isn’t the only planet in the HD 219134 system. There are actually two others orbiting the same star. There is a planet that is about 2.7 times the mass of Earth and another that is 8.7 times the mass. These orbit the star at distance of 6.8 days and 46.8 days respectively. At these sizes, these planets are not likely terrestrial but are probably gas planets, similar to Uranus or Neptune. The second planet at 2.7 times the mass of Earth may be small to be terrestrial but we don’t know yet.

Hopefully these planets are orbiting in a single plane like in our solar system so they are all in transit with us.

About Harry H

Harry H

Harry is currently studying biology and chemistry in University and hopes to go to grad school for evolutionary biology. He enjoys writing about sciences and sports and is a big fan of hockey and soccer. Some of his other interests are reading and rock climbing.
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  • T. McGrath

    HD 219134b is not the closest rocky exoplanet to Earth. The closest rocky exoplanet to Earth is Alpha Centauri Bb, located a distance of 4.366 light years away. Furthermore, it is doubtful that HD 219134b is rocky.

    “Most 1.6 Earth-Radius Planets are not Rocky” –

    • Harry H

      Thank you for your comment.

      While Alpha Centauri Bb is closer to Earth, it has not yet been confirmed. Here is the abstract of an article that describes why:
      NASA also posted an article similar to mine stating it is that closest confirmed rocky exoplanet to Earth.
      I will change the title of my article to say ‘closest confirmed exoplanet to Earth’
      The team who conducted the study estimated the density of the planet and concluded it was most likely rocky. Here is the abstract for that study:

      Thank you for taking the time to give me feedback.