StarDate

The Moon is passing through a well-known sign of the zodiac right now: Aquarius. Most of the stars that form the water bearer’s classical outline stand to the left of the Moon.

One recently discovered treasure in Aquarius is a star system that contains three Earth-sized planets.

TRAPPIST-1 is only 40 light-years from Earth — just down the block by stellar standards. The star is less than one-thousandth as bright as the Sun, though, so you need a good-sized telescope to see it.

The three planets orbit quite close to the star. And two of them appear to be just outside the bounds of the star’s habitable zone. That’s the distance from the star where temperatures are just right for liquid water, which is a key ingredient for life. But it’s possible that regions on these planets, which receive more or less starlight than average, could be habitable.

Astronomers are looking hard to find other Earth-size worlds in the habitable zones of other stars. These are the places where we’re most likely to find Earth-like life. So far, only a few planets are on the list. Most planets are outside the habitable zone, and many that are in the zone are big balls of gas, which are less likely to host life.

Some of those giants could have moons with the right conditions for life, though. In fact, so could planets outside the habitable zone. So some astronomers are starting to search not just for exoplanets, but for exomoons. More about that tomorrow.

Script by Damond Benningfield

Two planets glide down the southwestern sky this evening. Bright orange Mars is low in the south-southwest as night falls, with fainter Saturn to the right by about the width of your fist held at arm’s length.

These worlds represent different categories of planets. Mars is a small and rocky planet, like Earth, while Saturn is a big ball of gas.

Many of the thousands of planets found in other star systems fall into discrete categories as well. There are super-Earths, mini-Neptunes, super-Neptunes, super-Jupiters, and hot Jupiters.

Super-Earths are up to a few times the mass of Earth. They’re still balls of rock and metal, but they may be much denser than Earth.

Neptune is the most-distant planet in the solar system, and consists of layers of rock, ice, and gas. Mini-Neptunes are smaller than Neptune, but they have the same basic structure. Super-Neptunes are also put together like our Neptune, but they’re up to a few times more massive.

Super-Jupiters are more massive than our Jupiter, the giant of the solar system. They probably have dense cores enveloped by deep layers of gas. They’re about the same size as Jupiter, but up to several dozen times its mass.

Hot Jupiters were some of the first planets ever discovered. Such a world is similar to Jupiter, but much closer to its star. That can heat its outer atmosphere to thousands of degrees — creating a category of planets unlike anything in our own solar system.

More about exoplanets tomorrow.

Script by Damond Benningfield

It feels like every time astronomers even look at a star these days, they find a planet or two in orbit around it. They’ve confirmed about 3500 planets in all, with thousands more awaiting confirmation. The planets range from about the mass of the Moon to many times the mass of Jupiter, the largest planet in the solar system. Some are quite close to their parent stars, while others are far away. And some orbit a single star, while others have two suns in their sky — or even three.

One amazing thing about these discoveries is that, in an era of giant telescopes, most of the exoplanets were found with small telescopes.

Most of the planets were discovered with Kepler Space Telescope. The spacecraft looks for a small dip in a star’s light caused by a planet passing across its disk. And it does so with a main mirror that measures just three feet across — quite small by modern research standards.

Many ground-based planet searches are done with even smaller telescopes, which devote all their time to hunting planets. A robotic network known as HAT, for example, has discovered almost 60 planets with telescopes that consist of 200-millimeter camera lenses. And a telescope known as KELT-North, which uses an 80-millimeter lens, has discovered four confirmed planets.

These little telescopes are helping make some big discoveries about worlds in other star systems.

We’ll talk about some of the worlds these telescopes are finding tomorrow.

Script by Damond Benningfield

A radio telescope in a big bowl is about ready to get to work. Construction was finished in July, and scientists have spent the last couple of months checking it out.

The telescope is known as FAST. It was built in a natural bowl-shaped depression in south-central China. It’s 500 meters wide — almost a third of a mile. That makes it the second-largest single-dish radio telescope in the world.

FAST is patterned after the Arecibo Telescope in Puerto Rico, which is also built in a natural basin. The terrain makes it easier to support the telescope, which forms a wide, shallow dish. It also provides some shielding from radio interference here on Earth.

That design means the telescope can’t move to follow astronomical objects as Earth spins on its axis. Instead, a tracking system above the dish moves, allowing the telescope to keep an eye on an object for up to a few hours. That design comes with a trade-off, though — astronomers can’t use more than 300 meters of the radio dish at a time.

Astronomers already have several projects lined up for the telescope. They’ll use it to map clouds of gas that trace the spiral arms of the Milky Way galaxy, for example. They’ll also look for pulsars — the rapidly spinning corpses of dead stars. And they’ll search for radio signals from other civilizations — adding a new tool in the search for extraterrestrial intelligence.

We’ll talk about how some small telescopes are searching for other planets tomorrow.

Script by Damond Benningfield

Helium is the second-most abundant element in the universe. It accounts for about one out of every 12 atoms. Most of it was formed in the Big Bang, with the rest forged in the hearts of stars. In fact, the Sun converts more than 600 million tons of hydrogen to helium every second.

Yet here on Earth, helium is one of the rarest elements. It’s almost never found on its own. It’s usually mixed in with natural gas. And the few deposits that have been found are playing out. Production in the world’s biggest helium deposits, in the Texas Panhandle, has been declining for years. But there are many uses for helium — it lifts blimps, is used in rockets, and has many other uses in science and industry.

Scientists recently discovered a giant new helium field in Tanzania. They found it by using a technique that promises even more discoveries in the future.

Researchers from Norway and the UK suggested that volcanic activity can release the helium gas that’s mixed with other elements. They found a volcanic field in Tanzania that fit their profile. And when they drilled earlier this year, they struck helium. It’s the first helium deposit ever found intentionally — all the others were found during drilling for oil and gas.

It’ll take a while to start extracting the helium. But the scientists hope their technique will lead to new discoveries — making one of the most abundant elements in the universe a little easier to find here on Earth.

Script by Damond Benningfield

Earth’s Moon most likely formed as the result of a “big whack” — a collision between the young Earth and another planet. The impact blasted debris into space, which coalesced to form the Moon.

The moons of Mars may have formed in the same way.

Phobos and Deimos are small, oblong chunks of rock. The leading theory has been that they were asteroids that passed close to Mars, allowing the planet’s gravity to lock them into orbit. But not all astronomers agreed with that explanation. The composition of the moons didn’t seem quite right, for example. So the idea that they were born in a big whack has gained support in recent years.

It gained more support from two studies published in July. Researchers concluded that Mars was blasted by a smaller object within a few hundred million years of the planet’s birth. That spewed molten rock, bits of dust, and hot gas into orbit around Mars.

According to the simulations, molten rock close to the planet formed a large moon and several smaller ones, while gas and dust formed Phobos and Deimos farther from Mars. Mars’s gravity quickly pulled the closer moons back down, leaving only Phobos and Deimos. They’ve been spiraling closer to Mars ever since. And within 50 million years or so, Phobos, too, will slam into Mars — leaving the Red Planet with a single moon.

Look for Mars below our Moon this evening. The planet looks like a bright orange star. But you need a good telescope to see its two little moons.

Script by Damond Benningfield

There are many great examples of how astronomy has progressed in recent decades, from the discovery of dark energy to the confirmation of thousands of planets in other star systems.

For another example, consider the bright light below the Moon this evening: Saturn. Until the late 1970s, astronomers knew of only about 10 moons for the giant planet. Since then, the number has jumped to the 60s.

Some of those discoveries came from the twin Voyager spacecraft, which flew past Saturn in the early ’80s. Their cameras detected several small, dark satellites orbiting far from Saturn.

Other discoveries came more recently, from ground-based telescopes, mainly in Hawaii. Researchers spent years searching around Saturn and the other giant planets for previously unseen moons. Their efforts were rewarded with dozens of new moons. And finally, the Cassini spacecraft found a half-dozen more moons of Saturn early in this century.

None of these recently discovered worlds is anything special. Most are only a few miles in diameter. They’re oddly shaped chunks of rock — perhaps debris from bigger moons, or asteroids captured by Saturn’s gravity. Even so, they tell us a lot about the environment of the outer solar system — and about how quickly the science of astronomy is advancing.

Again, look for Saturn below the Moon this evening. The star Antares is below Saturn, with the brighter planet Mars to their left — a beautiful grouping in the evening sky.

Script by Damond Benningfield

At first glance, the asteroid Bennu seems pretty benign. It’s about a third of a mile across, and it’s probably a loose agglomeration of rock and ice. And because it contains a lot of carbon, it’s darker than a charcoal briquette. Yet Bennu isn’t quite as innocuous as it seems, as Arizona astronomer Ed Beshore explains:

BESHORE: It is one of the most threatening of all asteroids right now. It has roughly a one-in-a-thousand chance of hitting Earth late in the 22nd century, which is a pretty high chance when it comes to asteroid impacts.... It’s about a 500- to 600-meter-wide asteroid. Because of that, if it did hit the Earth, it would actually be a pretty destructive event. It probably wouldn’t be a civilization-threatening event, but it would be catastrophic.

Beshore is one of the lead scientists for a spacecraft that’s scheduled to study the asteroid. OSIRIS-Rex will launch as early as this week. After a long cruise, it’ll spend about two years flying along with Bennu. Then it’ll drop to the surface and pick up some dust and pebbles for return to Earth.

The main goal is to study the asteroid, which is a leftover from the birth of the planets. But a secondary goal is to develop techniques for maneuvering around an asteroid. Such techniques might be needed if Bennu or any other asteroid is found to be on a collision course with Earth — keeping our planet safe from one of the hazards of the solar system.

Script by Damond Benningfield

Anytime you make something, you can expect to have some raw materials left over. For a house, it’s nails and scraps of wood. For a dress, it’s scraps of fabric. And for the solar system’s planets, it’s chunks of ice and rock — the asteroids and comets that didn’t get incorporated into the planets.

Studying that debris can reveal important details about how the planets were born. And a new mission is expected to do just that.

OSIRIS-Rex is scheduled for launch as early as this week. It’ll spend a couple of years reaching its target, a small asteroid called Bennu. It’ll scan the asteroid from every angle, then touch down and scoop up some of the dust at its surface — anywhere from a few ounces to a few pounds. It’ll then bring that material back to Earth for analysis.

Ed Beshore is one of the project scientists:

BESHORE: The first job in the mission is to try to identify the materials that might be representative of the materials that the solar system was originally constructed from. So what we expect to find at our target asteroid is very pristine, very ancient solar system material....

What we’re really talking about doing is finding an object that may harbor information about what that original material was like, and also lead to important clues about where the Earth’s water came from and where some of the organics might have originated. Are the organics something that are unique to the Earth, or are they found even in these primitive bodies?

— learning about Earth’s past by studying some solar-system leftovers.

More about OSIRIS-Rex tomorrow.

Script by Damond Benningfield

After keeping company with a comet for the last two years, a spacecraft is about to get a whole lot closer to it. Engineers will nudge it to a gentle touchdown at the end of the month. That’ll provide the sharpest views of any comet to date.

Rosetta entered orbit around Comet 67P Churyumov-Gerasimenko in August of 2014. It dropped a probe a few months later, but the probe landed awkwardly and soon expired.

Even so, Rosetta revealed a great deal about the comet. It found that 67P is shaped like a rubber duck, with two lobes joined by a narrow neck. A recent study found that the two lobes may have split apart and come back together many times over the comet’s history.

Rosetta also measured the comet’s composition. It detected an amino acid and other compounds that are important for life, suggesting that comets might have delivered some of the ingredients for life to Earth. But it found that the water on 67P doesn’t match that found on Earth. That might mean that Earth’s water did not come from comets, as scientists have long suggested.

Over the next few weeks, Rosetta will drop closer and closer to the comet, then touch down, snapping pictures and taking other readings along the way. But it’s not designed as a lander, so its solar arrays won’t be able to gather sunlight, and its radio antenna won’t be able to aim at Earth — bringing its mission to an end.

A mission to an asteroid is just about to get started. More about that tomorrow.

Script by Damond Benningfield