Light as cotton candy

The University of Liège in Belgium discovered a planet with the same density as cotton candy. his name is WASP-193b It is the second planetLess dense than we knowBut her oddities do not end there.

As researchers pointed out in an article published in Nature astronomyThis planet is incomprehensible to our laws of physics. The body asks us to say that “according to science it should not exist,” but science is not responsible for determining whether something that has been discovered experimentally should exist or not, so, we are best left with the fact that it is not understood.

In other words, if we go from what science knows about planet formation, we don’t know how such a scattered planet could form. Because when we say it has the density of cotton candy, we’re not exaggerating. WASP-193b has a density of 0.059 grams per cubic centimeter while cotton candy has a density of 0.05 grams per cubic centimeter.

To give us an idea of ​​the difference compared to other planets, we can compare it with Jupiter, which is another fairly light giant. Although WASP-193b is approximately 50% larger than Jupiter (it is roughly the size of Jupiter and a half), its density is seven times less than that of our gas giant. How can we know?

Measuring the density of a planet isn’t easy, but when it’s not in our solar system, it becomes even more complicated. WASP-193b orbits a star with properties similar to our Sun, but it does so much faster. We know this because when the WASP-South Observatory was collecting night sky data from 2006 to 2008 and from 2011 to 2012, scientists detected a regular dip in the star’s brightness. Every 6.25 days reduce its intensity. From this they were able to deduce, through the so-called transit technique, the passage of a planet between us and the star, which leads to its regular eclipse, as well as its size.

Next, they used the TRAPPIST-Sur and SPECULOOS-Sur observatories to verify that the intervening object was indeed a planet. They then used spectroscopy to measure the planet’s mass using the HARPS and CORALIE spectrometers. Now that they know it is a planet and they know its size and density, they can conclude that they are facing the second known exoplanet with the lowest density, which is not easy considering that we already know more than one planet. 5000 exoplanets. How is that possible?

The key is air, just like in potato sacks. For some time now, the complaint that there is more air in potato bags than in potatoes has been widespread, and this is partly true. This would be true if we only considered volume and by air we meant the nitrogen in the bags (which is the main component of the air we breathe, but not the only one).

In this case, the air protects the potatoes from being crushed during transport in the bag, but it helps us visualize WASP-193b. The density of this bag of potatoes will be much lower than that of French fries, because a weighted average must be made between the amount of potatoes and the amount of gasBecause gas is much lighter than potatoes. In fact, the more air there is, other things being equal, the less dense it becomes.

Researchers suspect that the new planet consists mostly of hydrogen and helium. Until this moment there is no surprise, it is the same composition that our gas giants have, which if they were larger, would turn into stars.. However, in the case of WASP-193b, these gases form an extremely puffy atmosphere that extends tens of thousands of kilometers beyond the atmosphere we expect from Jupiter.

“We don’t know where to place this planet in all the theories of formation we have now, because it is an exception to them all. We cannot explain how this planet formed. “Taking a closer look at its atmosphere will allow us to determine the evolutionary path of this planet,” adds Francisco Pozuelos, an astronomer at the Institute of Astrophysics of Andalusia (IAA-CSIC, Granada, Spain).

Or as Khaled Al-Barqawi puts it: “WASP-193b is a cosmic mystery. Solving it will require further observational and theoretical work, especially to measure the properties of the atmosphere using the JWST space telescope and confront them with different theoretical mechanisms that might lead to such extreme inflation.

• The fact that known scientific theories do not allow us to predict the existence of something that we end up discovering experimentally does not mean that this thing should not exist. The trends and laws stated by science are not directive, but rather descriptive. There are scientific laws, which are those that we discover, and they are closer to natural laws to a greater or lesser degree, but they can be wrong, which is why they only try to describe what the natural laws command.

• “An extended, low-density atmosphere around the Jupiter-sized planet WASP-193 b.” Nature astronomy 10.1038/s41550-024-02259-y