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Nasa has spotted an exoplanet 13,000 light-years away, making it one of the most distant planet ever found.

Known as 'Ogle-2014-BLG-0124Lb,' the gas giant was detected by the Spitzer Space Telescope and the Ogle Warsaw Telescope in Chile.

The planet is half as massive as Jupiter and could help astronomers gain a better understanding of the distribution of planets in the Milky Way.

Astronomers have spotted one of the most distant planets ever found. Known as 'Ogle-2014-BLG-0124Lb,' the gas giant was detected by the Spitzer Space Telescope and the Ogle Warsaw Telescope in Chile. Most of planets we know about are around of 10-100 times closer

Most of planets we know about are around of 10-100 times closer than Ogle-2014-BLG-0124, claims Jennifer Yee of the Harvard-Smithsonian Center for Astrophysics.

'We don't know if planets are more common in our galaxy's central bulge or the disk of the galaxy, which is why these observations are so important,' she added.

The discovery demonstrates that Spitzer - from its unique perch in space - can be used to help solve the puzzle of how planets are spread out in our galaxy.

The planet was discovered using a technique known as microlensing.

This happens when one star happens to pass in front of another, and its gravity acts as a lens to magnify and brighten the more distant star's light.

If that foreground star happens to have a planet in orbit around it, the planet might cause a blip in the magnification.

Astronomers are using these blips to find and characterise planets tens of thousands of light-years away in the central bulge of our galaxy, where star crossings are more common.

Our sun is located in the suburbs of the galaxy, about two-thirds of the way out from the centre.

The microlensing technique as a whole has yielded about 30 planet discoveries so far, with the farthest residing about 25,000 light-years away.

'Microlensing experiments are already detecting planets from the solar neighborhood to almost the center of the Milky Way,' said co-author Andrew Gould of The Ohio State University, Columbus.

'And so they can, in principle, tell us the relative efficiency of planet formation across this huge expanse of our galaxy.'

This infographic explains how the Spitzer Space Telescope can be used in tandem with a telescope on the ground to measure the distances to planets. The planet was dicovered via microlensing which happens when one star passes in front of another, and its gravity acts as a lens to magnify the more distant star's light

Microlensing complements other planet-hunting tools, such as the Kepler mission, which has found more than 1,000 planets closer to home.

But it faces one key problem: This method can't always precisely narrow down the distance to the stars and planets being observed.

While a passing star may magnify the light of a more distant star, it rarely can be seen itself, making the task of measuring how far away it is challenging.

Of the 30 planets discovered with microlensing so far, roughly half cannot be pinned down to a precise location. The result is like a planetary treasure map lacking in X's.

That's where Spitzer can help out, thanks to its remote Earth-trailing orbit.

Spitzer circles our sun, and is currently about 128 million miles (207 million km) away from Earth. That's farther from Earth than Earth is from our sun.

When Spitzer watches a microlensing event simultaneously with a telescope on Earth, it sees the star brighten at a different time, due to the large distance between the two telescopes and their unique vantage points.

This technique is generally referred to as parallax.

'Spitzer is the first space telescope to make a microlens parallax measurement for a planet,' said Yee.

Data from the microlensing event is seen here.  If the foreground star is circled by a planet, the planet's gravity can alter the magnification over a shorter period, seen in the plot in the form of spikes and a dip

'Traditional parallax techniques that employ ground-based telescopes are not as effective at such great distances.'

Using space telescopes to observe microlensing events is tricky. Ground telescopes send out alerts to the astronomy community when an event starts, but the activity can quickly fade, lasting on average about 40 days.

In the case of the newfound planet, the duration of the microlensing event happened to be unusually long, about 150 days.

Both Spitzer and Ogle's telescopes detected the telltale planetary blip in the magnification, with Spitzer seeing it 20 days earlier.

This time delay between viewing of the event by Ogle and Spitzer was used to calculate the distance to the star and its planet.

Knowing the distance allowed the scientists also to determine the mass of the planet, which is about half that of Jupiter.

'We've mainly explored our own solar neighborhood so far,' said Sebastiano Calchi Novati, a Visiting Sagan Fellow at Nasa's Exoplanet Science Institute.

'Now we can use these single lenses to do statistics on planets as a whole and learn about their distribution in the galaxy.'