Not everything is as it seems — for exoplanets, at least.

Some exoplanets are actually smaller than what scientists pegged them to be, a new research suggests. In fact, the size of most exoplanets may be consistently overestimated.

What's the culprit? It's all because of atmospheric clouds and haze.

Compare And Contrast

Nowadays, astronomers in their respective observatories all over the world have become skilled enough to spot exoplanets, even those that are thousands of light-years away.

However, gathering details such as the size, mass and composition of the exoplanets still remains a great challenge for scientists.

Now, in order to better understand the accuracy of exoplanets observations, researchers from the Space Research Institute of the Austrian Academy of Sciences took a closer look at two low-mass exoplanets that seem similar.

The two exoplanets orbit their host star for five and 12 days, respectively. Both planets are also roughly the same size.

One planet is four times the diameter of Earth, while the other is five times that of our planet's diameter.

The inner exoplanet is less than six times Earth's mass, while the outer planet is 28 times as massive as Earth.

Their similarity in size only suggests that the inner planet has quite a low density. Each planet's quick orbit also meant that both planets are close to their host sun and should experience extreme heat.

Astronomer Helmut Lammer and his fellow scientists learned, that if one of the exoplanets is as big as it looks, the smaller one would burn off its atmosphere over the course of 100 million years.

However, their host star is billions of years old, so the smaller planet theoretically should have lost its atmosphere a long time ago.

The team concluded that the exoplanet is only about half as big as it seems.

Indeed, a smaller planet with an extended, wispy atmosphere that contains high-altitude features could definitely confuse astronomical observations, says Lammer.

He says the radius is based on what scientists see when the exoplanet makes its transit. This transit is likely distorted by haze and clouds high in the atmosphere, in a region where atmospheric pressure is otherwise low.

Caution During Measurements

As of writing, scientists have already identified more than 3,000 exoplanets, and this number will continue to increase as observations and research becomes even more efficient at searching for candidates.

In light of the study's findings, Lammer suggests that scientists should review the results of past exoplanet surveys, like those conducted by NASA's Kepler observatory.

Luca Fossati, co-author of the study, says astronomers — especially those who are part of the European Space Agency's new program called Characterizing Exoplanets Satellite — need to be cautious about initial measurements.

Fossati says since Kepler has detected several low-density and low-mass planets that are similar, it is highly likely that the size for many of them differ from the true value.

"There could be a bias in the results," says Fossati.

Details of the new study are published in the Monthly Notices of the Royal Astronomical Society.