First images of a planet outside our Solar System

What are exoplanets?

The search for planets orbiting other stars has long fascinated astronomers. Is the Solar System with its collection of gas giants and rocky planets common in the Milky Way, is it rare, or is it unique?

The first confirmation of a planet outside the Solar System or “exoplanet” actually occurred back in 1917,  but wasn’t recognised as such for nearly another 100 years. 

The discovery of the first exoplanet was announced early in 1992.  Since then, there’s been well over 5,000 planets discovered orbiting other stars in the Milky Way (and some even in other galaxies). There are many Earth-like planets with solid surfaces and gas giants like the planets found in our own Solar System.

A good place to keep up to date with the latest in exoplanet discoveries is exoplanets.nasa.gov

There is some debate even on the rough number of planets in our galaxy, but one estimate puts the number of planets in the Milky Way at around 100 billion – of which some 300 million are rocky planets like the Earth.

Finding exoplanets

Several problems made finding and observing exoplanets a complex and time consuming problem. Firstly, the light shining from the host star is vastly brighter than the light reflecting off the surface of the planets orbiting it. In the case of the Earth, the Sun would appear over a billion times brighter than our planet for would be planet hunters in other parts of the Milky Way. The glare from the host stars overwhelms even sensitive instruments.

Because of reasons like these, exoplanets have been found using a variety of techniques including measuring light dips in the star they orbit as they cross in front of it and even how much planets cause the host star to “wobble” during their orbits.

The first confirmed exoplanet was found to be orbiting the millisecond pulsar, PSR B1257+12. This is a kind of fast rotating neutron star. PSR B1257+12 spins at some 9,650 rpm and a small irregularity in the star’s spin was found to be the cause of a gravitational “tug” of a planet orbiting it. (There are now three planets confirmed to be orbiting the star.)

In 1995, 51 Pegasi b was the first exoplanet discovered orbiting a main sequence star. (This is a star like the Sun going through its normal lifecycle and the kind that we see in the night sky). What surprised astronomers is the large size and short orbital period of 51 Pegasi b. Its year is just over four Earth days! Given its closeness to the star and its size, 51 Pegasi b was classified as a “Hot Jupiter” and the example for other planets like this. It was discovered by observing small shifts in the spectrum of the nearby star. There’s been some claims of direct observation the planet, but these are not fully confirmed. (More on 51 Pegasi b here ).

An artist’s impression of 51 Pegasi b/via ESO

Over 5,000 other exoplanets have been found over the last few decades by both ground based and dedicated orbiting observatories like TESS . These have even been exoplanets discovered orbiting stars in other galaxies.

Can we see exoplanets?

Despite all these exoplanet discoveries, observation of them has proved difficult.  Some have been discovered by a process called Direct Imaging  – the detection of light reflected off the planet by the host star – but this has been used to find only a few dozen of the thousands found by other methods.  This has been likened to finding a firefly next to a floodlight.

While astronomers using the largest ground based telescope have able to “see” exoplanets, any detail on their surface cannot be resolved yet. (I remember reading articles in the past stating the this is something humans would never be able to achieve as even the nearest exoplanets would require incredibly massive telescopes view them!)

Exoplanet 2M1207b near its host star imaged in the Infrared/via ESO

Is the JWST looking for exoplanets?

One of the primary mission objectives for the JWST is not just to detect exoplanets, but even to observe them in detail and carry out analysis of their atmospheres. Are there exoplanets capable of sustaining life? Are there any with signs of biological processes?  (JWST has already detected carbon dioxide in the atmosphere of an exoplanet. Read more here )

In yet another remarkable “first”, the James Webb Space Telescope (JWST) has taken the first direct image of a planet outside the Solar System during one of its early attempts at observing exoplanets. HIP 65426 b is a young planet, some 6-12 times the mass of Jupiter.

Image of HIP 65426 b taken with the JWST

The shape of the planet appears slightly different in each image due to the way different instruments on the JWST handle various wavelengths.  The “star” in each image is from the coronagraph in the instruments which helps to out light from the host star.

These images have been produced earlier than expected by the JWST mainly as the telescope is performing better than astronomers had planned for and point to some revolutionary discoveries in the field of exoplanet research in the coming years.

Q. Can I see exoplanets with my telescope.

A. It’s pretty much a big no on that one.

BUT – there are some great programs for serious amateur astronomer to get involved in exoplanet research, like NASA’s Exoplanet Watch.

Cheers,

Earl White

BINTEL

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