StarDate

Until almost a century ago, the constellations were little more than stick figures. Various astronomers connected different dots to define their characters. And they used different borders to define each constellation’s chunk of celestial real estate.

Order was imposed upon the heavens in 1930. Belgian astronomer Eugene Delporte defined the borders of 88 official constellations for the International Astronomical Union. Those borders have been maintained ever since.

The list of constellations includes Aries, the ram. It’s well up in the east as night falls now, and stands due south a few hours later.

Despite its fame as a member of the zodiac, Aries includes only three bright stars. A fourth star is added to those to create a stick figure that looks like a lopsided boomerang.

But the formal constellation covers a much wider area – about one percent of the entire sky. It looks like a horizontal rectangle with chunks missing from the lower left and top right corners.

Its borders consist of 12 individual lines. When Delporte drew those borders, they followed strict lines of declination and right ascension – the equivalent of latitude and longitude on Earth.

Since then, thanks to a wobble in Earth’s axis, the borders have shifted position a little bit. So some day, astronomers will have to redefine the borders – or watch as the stars of all the constellations shift across the borders of their neighbors.

Script by Damond Benningfield

Mars and Jupiter are siblings – planets born at the same time, from the same disk of debris around the infant Sun. And they’re fairly close together – the fourth and fifth planets out. But other than that, they don’t seem to have much in common. They don’t look alike, their composition is different, and they’re wildly different sizes.

The two planets will huddle close together in the morning sky the next few days. They climb into good view by about one o’clock, and are high in the sky at dawn. Jupiter looks like a brilliant star. Mars is just above it as they rise tomorrow, but will slide past Jupiter over the following few days. At their closest, they’ll be separated by about one degree – the width of a pencil held at arm’s length.

Jupiter is the largest and heaviest planet in the solar system – about 11 times the diameter of Earth. It’s a big ball of gas with a small, dense core. It formed far enough from the Sun that it was surrounded by lots of ice and gas, which it pulled in to grow to its enormous proportions.

Mars is only a little more than half of Earth’s diameter – roughly five percent the diameter of Jupiter. It’s a dense ball of rock and metal. It formed much closer to the Sun, where there was much less ice and gas. And Jupiter’s gravity might have stirred up things where Mars was born, limiting its growth. So Mars remained small – a mere fraction the size of its giant sibling.



Script by Damond Benningfield

Our solar system is filled with millions of leftovers – the chunks of rock and ice that weren’t incorporated into the planets and moons. The icy ones are known as comets, while the rocky ones are asteroids. But there’s not that much difference between them. They have similar ingredients, but in different amounts. How we classify them has more to do with where they were born and how close they get to the Sun.

The planets formed from a disk of material that encircled the infant Sun. Small grains of ice and rock stuck together to make larger bodies. These larger objects then stuck together to make the planets and some of their moons.

In the outer solar system, it was cold enough for these building blocks to contain a lot of ice. But closer to the Sun it was hotter, so the building blocks consisted mainly of rock and metal.

The outer planets kicked many of the leftovers deeper into space. One of them occasionally falls toward the Sun. Solar energy vaporizes some of the ice, releasing some of the solid particles as well. The Sun pushes some of this gas and dust away, forming a long, bright tail – a comet.

Many asteroids have a fair amount of ice as well, just not enough to make a tail. Most asteroids are concentrated in a broad belt between Mars and Jupiter. About one-and-a-half million have been cataloged, with millions more awaiting discovery – leftovers from the birth of the solar system.

Script by Damond Benningfield

If anyone ever makes it to Pluto, they might want to stay away from the bottoms of steep craters. Occasional jiggling and shaking on the surface might trigger big, fast landslides – some of them big enough to bury a small city.

Planetary scientists recently found evidence of several massive pileups in images snapped by New Horizons. The spacecraft flew past Pluto in 2015, giving us our only close look at everyone’s favorite dwarf planet.

The aftermath of six landslides was detected on the inner slopes of three craters. All of the craters are near the edge of Sputnik Planitia, a heart-shaped ice plain that’s Pluto’s most prominent feature. The images revealed either fields of large boulders or indentations in the crater walls where material had slumped away.

Because of Pluto’s weak gravity and icy surface, the slides traveled a long way. Material slid from about six to nine miles before coming to rest, and dropped up to a mile and a half from a crater’s rim to its floor. The largest slide covered an area large enough to bury Boston or Fargo.

One of the landslides could have been triggered by an impact that gouged a small crater near the edge of the crater that contained the debris. The others could have been powered by temperature changes. Some of the ices at the surface vaporized, weakening the crater walls. So whatever the cause, it might be wise to stay away from the slopes of Pluto’s craters.

Script by Damond Benningfield

Two “super-puff” planets appear to orbit a bright star about 1100 light-years from Earth. They’re as big as Jupiter, the giant of our own solar system. But they’re only a few percent the mass of Jupiter. That makes them extremely puffy – the least-dense worlds yet seen – less dense than cotton candy. Such planets are called super-puffs.

The planets orbit the star TOI 791. It’s a little bigger and heavier than the Sun, and a few times brighter. But it’s too far south to see from all but a sliver of the United States.

The planets were discovered by TESS, a planet-hunting space telescope. But it took years for astronomers to winnow out their details. They used almost a dozen ground-based telescopes, including one near the south pole.

The planets periodically pass in front of their star, dimming the star’s light. But the gravity of each planet tugs at the other, changing the timing of these transits. The scope of the change revealed the masses of the planets.

One planet orbits at a little less than the distance from Earth to the Sun, while the other is a bit closer. They might have been born farther out, then migrated to their current spots – a scenario that could explain their puffiness.

Astronomers plan to study the system with James Webb Space Telescope. It can reveal the composition of the planets’ atmospheres, telling us more about where the planets formed – and how they became super-puffs.



Script by Damond Benningfield