StarDate

The closer we look at the worlds of the solar system, the more places we see that could be homes for life. Some of those worlds orbit Jupiter, the largest planet in the solar system. Jupiter itself isn’t on the list. It’s a big ball of gas with no solid surface. There has been speculation that large organisms could float through its skies. But that’s considered a long shot. It’s more likely that life could inhabit some of Jupiter’s moons. The leading candidate is Europa. It’s about the same size as our own moon. A deep ocean of liquid water probably lies below its icy crust. Plumes of hot water may squirt into the bottom of the ocean. The plumes would contain a variety of compounds – perhaps including the chemistry of life. So Europa has the right combination of water, heat, and chemistry to support life – at least microscopic life. Europa isn’t the only Jovian moon with a deep ocean. The largest moon, Ganymede, may have more liquid water than all Earth’s oceans combined. One other big moon may have an ocean as well. But the crusts of these moons are much thicker than Europa’s. So even if their oceans are inhabited, it’ll be much harder for us to find evidence of life. Look for Jupiter in the eastern sky in early evening, and arcing high across the sky later on. It looks like a brilliant star. Through binoculars, its big moons look like tiny stars quite close to the planet. More about Jupiter tomorrow. Script by Damond Benningfield

Jupiter looks like it’s wearing zebra stripes. Bands of clouds that run parallel to the equator alternate between bright and dark – zebra stripes. Each one is thousands of miles wide. The stripes are a result of Jupiter’s composition and its rotation. It’s basically a ball of gas – it’s made almost entirely of hydrogen and helium. And even though it’s 11 times the diameter of Earth, it spins on its axis in less than 10 hours. That forces the clouds that top its atmosphere into bands that stretch from east to west. The bands alternate between belts and zones. The belts are darker – probably because they allow us to see deeper into the atmosphere. The zones are topped by the highest clouds. The clouds are made of frozen ammonia, which looks bright white. The belts don’t have that layer. Instead, we’re seeing clouds in the next layer down. Those clouds are made of water and other compounds, which are darker. The stripes are flanked by jet streams that blow in alternating directions. They can roar at hundreds of miles per hour. They keep the belts and zones separated – maintaining the zebra stripes on this giant planet. Jupiter is at its best this week. It’s in view all night, and it shines brightest for the year. It looks like a brilliant star. It’s low in the eastern sky in early evening, and climbs high across the sky later on. The stripes are easily visible through just about any telescope. Script by Damond Benningfield

If today is your birthday, then Happy Birthday! The next one is just one year away – 365 sunrises and sunsets. If today is your birthday and you happen to be from Jupiter – well, Happy Birthday, and … we’re sorry. Your next one is almost 12 Earth years away – almost 10,500 sunrises and sunsets. The Jovian year is so long for a couple of reasons. First, the planet is more than five times farther from the Sun than Earth is. So its path around the Sun is more than five times longer than Earth’s. The second reason is the laws of orbital motion. The farther a planet is from the Sun, the slower its orbital speed. At Jupiter’s great range, it moves at less than half the speed of Earth. Ergo, one Jovian year lasts almost 12 Earth years. But to get all those sunrises and sunsets, you also have to factor in the length of a Jovian day. Although Jupiter is 11 times the diameter of Earth, it spins in a hurry – a day lasts less than 10 hours. Add it all up, multiply, divide, and carry the two, and – well, it’s a lot of days between birthdays on the Sun’s largest planet. Jupiter is especially vibrant now. It reaches opposition this weekend – it lines up opposite the Sun in our sky. It rises around sunset and is in view all night. The planet is also closest to us, so it shines at its brightest. In fact, in all the night sky right now, only the Moon outshines it. More about Jupiter tomorrow. Script by Damond Benningfield

Stars are born when giant clouds of gas and dust break apart and collapse. And if that’s all there was to it, the Milky Way Galaxy would give birth to a couple of hundred stars every year. Instead, thanks to feedback from the stars themselves, it makes only a few. Feedback is a process that clears away the material for making stars, but can also trigger the birth of more stars. Young stars, for example, produce winds and jets that blow away the gas and dust around them. Since stars are born in clusters, many youngsters can be sweeping away the star-making material at the same time. That pares back the number of stars that can be born in a cluster. Mature stars add to the feedback – not only with winds, but also with radiation. Hot stars generate a lot of ultraviolet energy. It vaporizes tiny particles of dust – eliminating possible building blocks for new stars. The heaviest stars explode as supernovas. These blasts can clear out the space for light-years around, creating big, empty bubbles. And supernovas also accelerate subatomic particles around them to almost the speed of light. These “cosmic rays” help to sweep away the raw material for making more stars. But supernovas can also enhance the birth rate. Their shock waves can cause distant clouds of gas and dust to collapse to form stars. So feedback is a complex process – one that both aids and hinders the birth of new stars. Script by Damond Benningfield

The planet Venus is switching sides today – sides of the Sun. It’s crossing behind the Sun as seen from Earth, so it’s moving from the morning sky to the evening sky. But we won’t be able to see it for several weeks. Venus is the second planet from the Sun, while Earth is third. So Venus crosses both behind the Sun and between Earth and the Sun. It switches between Morning Star and Evening Star appearances each time. Each of these crossings happens every 584 days – about 19 and a half months. The planet spends about eight months in both the morning and evening sky, and disappears from view during the crossings. When Venus passes between Earth and the Sun, it’s closest to us, so it moves across the sky quickly – it’s hidden in the Sun’s glare for only a few days. When it’s behind the Sun, it’s farthest – about 160 million miles. Because of the relative motions of Earth and Venus, it moves across the sky quite slowly. So it remains hidden in the light for three months or so. Depending on your location, Venus could emerge as the Evening Star as early as mid- to late February. It’ll be quite low in the twilight, so it won’t be easy to find. The planet will climb into better view in early March. Venus will reign over the evening sky until October, when it will vanish in the sunlight as it once again switches sides. Tomorrow: slowing down the stellar birth rate. Script by Damond Benningfield