A spacecraft exploring the wild ways of our magnificent sun has captured a rarely seen event from our position on the Earth’s surface. On January 3, 2023, under the guidance of the European Space Agency, Solar Orbiter observed the Solar System’s deepest planet gliding over the Solar disk; a small black spot against the background of raging flames.

This type of event is known as a transit and occurs when a smaller object, such as a planet or moon, crosses a star and blocks a small amount of its light. Although an orbiting object is often reduced to just a shadow, transit events can teach us all kinds of interesting things.

If you’ve heard the term recently, it’s probably because it’s the main tool on the set for finding planets or exoplanets outside the solar system. Space telescopes like Kepler and TESS have long looked at the stars to look for weak, regular dips that are a sign of a transiting exoplanet in starlight.

This subtle flicker of the shadow not only reveals the presence of the orbiting object, but could potentially provide a clue as to its composition. When an exoplanet – or even a closer planet like Mercury, or a moon for that matter – passes in front of its parent star, some of the star’s light seeps through any atmosphere it may have. Analyzing how the light differs from starlight could allow scientists to determine the composition of the gas.