Learn what to look for in the night sky with today's Nerdy Curio from Stardate. Two siblings with little family resemblance are getting together for a bit of a reunion right now. They’re in the east at first light, and they’re so bright and so close together that you just can’t miss them.

The brighter of the siblings is Jupiter, while the other is Mars. Fainter orange Mars will stand a bit to the right of Jupiter tomorrow. But Jupiter will have moved above Mars by the next day, with the two worlds still separated by just a fraction of a degree.

Jupiter is the largest planet in the solar system — about 11 times Earth’s diameter. Mars, on the other hand, is only a bit more than half the size of Earth.

The main reason for the difference is that the planets were born in different parts of the solar system.

Mars was born close to the Sun, where it was bathed in solar radiation and a strong “wind” of charged particles. That swept away much of the planet-making materials — hydrogen and helium gas, and frozen water and other ices. That left less material to make planets — bits of relatively heavy elements.

Jupiter was born several times farther from the Sun. Temperatures were colder there, and the solar wind was less intense. Small bits of rock and ice stuck together to make larger bodies, which in turn stuck together to make the core of Jupiter. As the planet grew, its gravity swept up lots of hydrogen and helium, surrounding the core with gas.

So Jupiter grew to immense proportions, while Mars stayed fairly scrawny.

Script by Damond Benningfield

Aired January 5, 2018

All Stardate content is available at stardate.org