The Basics

“Is there life on Mars?” is a question people have asked for more than a century. But in order to finally get the answer, we have to know what to look for and where to go on the planet to look for evidence of past life. With the Perseverance rover set to land on Mars on February 18, 2021, we are finally in a position to know where to go, what to look for, and knowing whether there is, or ever was, life on the Red Planet.

Credit: 

John Grant

Center for Earth and Planetary Studies

Si.edu

https://airandspace.si.edu/stories/editorial/percy-life-on-mars

If all goes according to plan, the landing of the Mars 2020 Perseverance rover (“Percy”) tomorrow (February 18, 2021) will mark the start of NASA’s ninth surface mission on the Red Planet. Percy will touch down in Jezero crater on Mars, where she will set off exploring new and uncharted terrains in search of ancient signs of life. Nearly 60 years have passed since the first spacecraft were sent to Mars, and it’s inspiring (albeit sometimes unbelievable) to reflect on the progress that has been made since then. First, we sent spacecraft to fly-by, then to orbit, then to land, and finally to rove. As we’ve become more familiar with Mars over time, and as our technological capabilities have improved, our methods of and goals for exploration have evolved in turn.  And with each new mission, humans have pushed the boundaries a little more—or in the case of Percy, a lot more. Here I highlight three new (and particularly challenging) aspects of the Mars 2020 mission that distinguish it from previous missions and that have the potential to significantly impact the future of Mars exploration.

Credits: Mariah Baker, si.edu

https://airandspace.si.edu/stories/editorial/driving-mars-exploration-perseverance

After glimpsing faint but widespread super-heated material in the Sun’s outer atmosphere, a NASA sounding rocket is going back for more. This time, they’re carrying a new instrument optimized to see it across a wider region of the Sun.

The mission, known as Extreme Ultraviolet Normal Incidence Spectrograph, or EUNIS for short, will launch from the White Sands Missile Range in New Mexico. The launch window opens on May 18, 2021.

EUNIS is an instrument suite mounted on a sounding rocket, a type of space vehicle that makes short flights above Earth’s atmosphere before falling back to Earth. Getting to space is important, because EUNIS observes the Sun in a range of extreme ultraviolet light that does not penetrate Earth’s atmosphere.

For the upcoming flight, the fourth for the EUNIS instrument, the team added a new channel to measure wavelengths between nine and 11 nanometers. (Visible light wavelengths are between 380 and 700 nanometers.)  The new wavelength range is attracting attention after an unexpected finding from EUNIS’s previous flight in 2013.

Credit: NASA

Astronomers have detected X-rays from Uranus for the first time, using NASA’s Chandra X-ray Observatory. This result may help scientists learn more about this enigmatic ice giant planet in our solar system.

Uranus is the seventh planet from the Sun and has two sets of rings around its equator. The planet, which has four times the diameter of Earth, rotates on its side, making it different from all other planets in the solar system. Since Voyager 2 was the only spacecraft to ever fly by Uranus, astronomers currently rely on telescopes much closer to Earth, like Chandra and the Hubble Space Telescope, to learn about this distant and cold planet that is made up almost entirely of hydrogen and helium.

In the new study, researchers used Chandra observations taken in Uranus in 2002 and then again in 2017. They saw a clear detection of X-rays from the first observation, just analyzed recently, and a possible flare of X-rays in those obtained fifteen years later. The main graphic shows a Chandra X-ray image of Uranus from 2002 (in pink) superimposed on an optical image from the Keck-I Telescope obtained in a separate study in 2004. The latter shows the planet at approximately the same orientation as it was during the 2002 Chandra observations.

What could cause Uranus to emit X-rays? The answer: mainly the Sun. Astronomers have observed that both Jupiter and Saturn scatter X-ray light given off by the Sun, similar to how Earth’s atmosphere scatters the Sun’s light. While the authors of the new Uranus study initially expected that most of the X-rays detected would also be from scattering, there are tantalizing hints that at least one other source of X-rays is present. If further observations confirm this, it could have intriguing implications for understanding Uranus.

One possibility is that the rings of Uranus are producing X-rays themselves, which is the case for Saturn’s rings. Uranus is surrounded by charged particles such as electrons and protons in its nearby space environment. If these energetic particles collide with the rings, they could cause the rings to glow in X-rays. Another possibility is that at least some of the X-rays come from auroras on Uranus, a phenomenon that has previously been observed on this planet at other wavelengths.

Credit: NASA

Earth is on a budget – an energy budget. Our planet is constantly trying to balance the flow of energy in and out of Earth’s system. But human activities are throwing that off balance, causing our planet to warm in response.

Radiative energy enters Earth’s system from the sunlight that shines on our planet. Some of this energy reflects off of Earth’s surface or atmosphere back into space. The rest gets absorbed, heats the planet, and is then emitted as thermal radiative energy the same way that black asphalt gets hot and radiates heat on a sunny day. Eventually this energy also heads toward space, but some of it gets re-absorbed by clouds and greenhouse gases in the atmosphere. The absorbed energy may also be emitted back toward Earth, where it will warm the surface even more.

Adding more components that absorb radiation – like greenhouse gases – or removing those that reflect it – like aerosols – throws off Earth’s energy balance, and causes more energy to be absorbed by Earth instead of escaping into space. This is called a radiative forcing, and it’s the dominant way human activities are affecting the climate.

Climate modelling predicts that human activities are causing the release of greenhouse gases and aerosols that are affecting Earth’s energy budget. Now, a NASA study has confirmed these predictions with direct observations for the first time: radiative forcings are increasing due to human actions, affecting the planet’s energy balance and ultimately causing climate change. The paper was published online March 25, 2021, in the journal Geophysical Research Letters.

“This is the first calculation of the total radiative forcing of Earth using global observations, accounting for the effects of aerosols and greenhouse gases,” said Ryan Kramer, first author on the paper and a researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland, Baltimore County. “It’s direct evidence that human activities are causing changes to Earth’s energy budget.”

NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project studies the flow of radiation at the top of Earth’s atmosphere. A series of CERES instruments have continuously flown on satellites since 1997. Each measures how much energy enters Earth’s system and how much leaves, giving the overall net change in radiation. That data, in combination with other data sources such as ocean heat measurements, shows that there’s an energy imbalance on our planet.

“But it doesn’t tell us what factors are causing changes in the energy balance,” said Kramer.

This study used a new technique to parse out how much of the total energy change is caused by humans. The researchers calculated how much of the imbalance was caused by fluctuations in factors that are often naturally occurring, such as water vapor, clouds, temperature and surface albedo (essentially the brightness or reflectivity of Earth’s surface). For example, the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua satellite measures water vapor in Earth’s atmosphere. Water vapor absorbs energy in the form of heat, so changes in water vapor will affect how much energy ultimately leaves Earth’s system. The researchers calculated the energy change caused by each of these natural factors, then subtracted the values from the total. The portion leftover is the radiative forcing.

Credit: NASA

NASA is targeting no earlier than April 8 for the Ingenuity Mars Helicopter to make the first attempt at powered, controlled flight of an aircraft on another planet. Before the 4-pound (1.8-kilogram) rotorcraft can attempt its first flight, however, both it and its team must meet a series of daunting milestones.

Ingenuity remains attached to the belly of NASA’s Perseverance rover, which touched down on Mars Feb. 18. On March 21, the rover deployed the guitar case-shaped graphite composite debris shield that protected Ingenuity during landing. The rover currently is in transit to the “airfield” where Ingenuity will attempt to fly. Once deployed, Ingenuity will have 30 Martian days, or sols, (31 Earth days) to conduct its test flight campaign.

“When NASA’s Sojourner rover landed on Mars in 1997, it proved that roving the Red Planet was possible and completely redefined our approach to how we explore Mars. Similarly, we want to learn about the potential Ingenuity has for the future of science research,” said Lori Glaze, director of the Planetary Science Division at NASA Headquarters. “Aptly named, Ingenuity is a technology demonstration that aims to be the first powered flight on another world and, if successful, could further expand our horizons and broaden the scope of what is possible with Mars exploration.”

Flying in a controlled manner on Mars is far more difficult than flying on Earth. The Red Planet has significant gravity (about one-third that of Earth’s) but its atmosphere is just 1% as dense as Earth’s at the surface. During Martian daytime, the planet’s surface receives only about half the amount of solar energy that reaches Earth during its daytime, and nighttime temperatures can drop as low as minus 130 degrees Fahrenheit (minus 90 degrees Celsius), which can freeze and crack unprotected electrical components.

To fit within the available accommodations provided by the Perseverance rover, the Ingenuity helicopter must be small. To fly in the Mars environment, it must be lightweight. To survive the frigid Martian nights, it must have enough energy to power internal heaters. The system – from the performance of its rotors in rarified air to its solar panels, electrical heaters, and other components – has been tested and retested in the vacuum chambers and test labs of NASA’s Jet Propulsion Laboratory in Southern California.

“Every step we have taken since this journey began six years ago has been uncharted territory in the history of aircraft,” said Bob Balaram, Mars Helicopter chief engineer at JPL. “And while getting deployed to the surface will be a big challenge, surviving that first night on Mars alone, without the rover protecting it and keeping it powered, will be an even bigger one.”

Credit: NASA

The near-Earth object was thought to pose a slight risk of impacting Earth in 2068, but now radar observations have ruled that out.

After its discovery in 2004, asteroid 99942 Apophis had been identified as one of the most hazardous asteroids that could impact Earth. But that impact assessment changed as astronomers tracked Apophis and its orbit became better determined.

Now, the results from a new radar observation campaign combined with precise orbit analysis have helped astronomers conclude that there is no risk of Apophis impacting our planet for at least a century.

Estimated to be about 1,100 feet (340 meters) across, Apophis quickly gained notoriety as an asteroid that could pose a serious threat to Earth when astronomers predicted that it would come uncomfortably close in 2029. Thanks to additional observations of the near-Earth object (NEO), the risk of an impact in 2029 was later ruled out, as was the potential impact risk posed by another close approach in 2036. Until this month, however, a small chance of impact in 2068 still remained.

When Apophis made a distant flyby of Earth around March 5, astronomers took the opportunity to use powerful radar observations to refine the estimate of its orbit around the Sun with extreme precision, enabling them to confidently rule out any impact risk in 2068 and long after.

Credit: NASA

In the quest for habitable planets beyond our own, NASA is studying a mission concept called Pandora, which could eventually help decode the atmospheric mysteries of distant worlds in our galaxy. One of four low-cost astrophysics missions selected for further concept development under NASA’s new Pioneers program, Pandora would study approximately 20 stars and exoplanets – planets outside of our solar system – to provide precise measurements of exoplanetary atmospheres.

This mission would seek to determine atmospheric compositions by observing planets and their host stars simultaneously in visible and infrared light over long periods. Most notably, Pandora would examine how variations in a host star’s light impacts exoplanet measurements. This remains a substantial problem in identifying the atmospheric makeup of planets orbiting stars covered in starspots, which can cause brightness variations as a star rotates.

Pandora is a small satellite mission known as a SmallSat, one of three such orbital missions receiving the green light from NASA to move into the next phase of development in the Pioneers program. SmallSats are low-cost spaceflight missions that enable the agency to advance scientific exploration and increase access to space. Pandora would operate in Sun-synchronous low-Earth orbit, which always keeps the Sun directly behind the satellite. This orbit minimizes light changes on the satellite and allows Pandora to obtain data over extended periods. Of the SmallSat concepts selected for further study, Pandora is the only one focused on exoplanets.

“Exoplanetary science is moving from an era of planet discovery to an era of atmospheric characterization,” said Elisa Quintana, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the principal investigator for Pandora. “Pandora is focused on trying to understand how stellar activity affects our measurements of exoplanet atmospheres, which will lay the groundwork for future exoplanet missions aiming to find planets with Earth-like atmospheres.”

Credit: NASA

Astronauts who have gazed at Earth from space have been awestruck at our blue marble planet's majesty and diversity. Mike Massimino, who helped service the Hubble Space Telescope in orbit, said, "I think of our planet as a paradise. We are very lucky to be here."

What's mind-blowing is that astronomers estimate there could be as many as 1 billion other planets like Earth in our Milky Way galaxy alone. Just imagine, one billion – not million – other "paradise planets." But it's paradise lost if nothing is living there to marvel at sunsets in azure blue skies. And, as 19th century philosopher Thomas Carlyle mused, "…what a waste of space."

It is sobering that our home planet is the only known place in the universe where life as we know it exists and thrives. And so, we gaze outward to the stars, imprisoned by space and time, into a cosmic loneliness. That's why scientists are dedicated to building ever-larger telescopes to search for potentially habitable planets. But how will they know life is present without traveling there and watching creatures walk, fly, or slither around?

One way is by probing a planet's atmosphere. An atmosphere with the right mix of chemical elements is necessary to nurture and sustain life. Earth's atmosphere includes oxygen, nitrogen, methane, and carbon dioxide that have helped support life for billions of years. Earth's abundance of oxygen, especially, is a clue that our atmosphere's oxygen content is being replenished by biological processes.

Astronomers have been using a variety of ground- and space-based telescopes to analyze how the ingredients of Earth's atmosphere look from space, using our planet as a proxy for studying extrasolar planets' atmospheres. They hope to eventually compare Earth's atmospheric composition with those of other worlds to note similarities and differences. Taking advantage of a total lunar eclipse, astronomers using the Hubble telescope have detected ozone in Earth's atmosphere by looking at Earthlight reflected off the Moon. Our Moon came in handy as a giant mirror in space.

Ozone is a key ingredient in our planet's atmosphere. It forms naturally when oxygen is exposed to strong concentrations of ultraviolet light, which triggers chemical reactions. Ozone is Earth's security blanket, protecting life from deadly ultraviolet rays.

This is the first time a total lunar eclipse was captured at ultraviolet wavelengths and from a space telescope. This method simulates how astronomers will search for circumstantial evidence of life beyond Earth by looking for potential biosignatures on extrasolar planets.

Using a space telescope for eclipse observations reproduces the conditions under which future telescopes would measure atmospheres of extrasolar planets that pass in front of their stars. These atmospheres may contain chemical signatures very similar to Earth, and pique our curiosity to wonder if we are not alone in the universe.

CREDITS:

Science: NASA, ESA, and A. Youngblood (Laboratory for Atmospheric and Space Physics)

STUDY FINDS THAT CAVITIES SCULPTED BY STELLAR OUTFLOWS DID NOT EXPAND OVER TIME

Stars aren't shy about announcing their births. As they are born from the collapse of giant clouds of hydrogen gas and begin to grow, they launch hurricane-like winds and spinning, lawn-sprinkler-style jets shooting off in opposite directions.

This action carves out huge cavities in the giant gas clouds. Astronomers thought these stellar temper tantrums would eventually clear out the surrounding gas cloud, halting the star's growth. But in a comprehensive analysis of 304 fledgling stars in the Orion Complex, the nearest major star-forming region to Earth, researchers discovered that gas-clearing by a star's outflow may not be as important in determining its final mass as conventional theories suggest. Their study was based on previously collected data from NASA's Hubble and Spitzer space telescopes and the European Space Agency's Herschel Space Telescope.

The study leaves astronomers still wondering why star formation is so inefficient. Only 30% of a hydrogen gas cloud's initial mass winds up as a newborn star.

Though our galaxy is an immense city of at least 200 billion stars, the details of how they formed remain largely cloaked in mystery.

Scientists know that stars form from the collapse of huge hydrogen clouds that are squeezed under gravity to the point where nuclear fusion ignites. But only about 30 percent of the cloud's initial mass winds up as a newborn star. Where does the rest of the hydrogen go during such a terribly inefficient process?

It has been assumed that a newly forming star blows off a lot of hot gas through light-saber-shaped outflowing jets and hurricane-like winds launched from the encircling disk by powerful magnetic fields. These fireworks should squelch further growth of the central star. But a new, comprehensive Hubble survey shows that this most common explanation doesn't seem to work, leaving astronomers puzzled.

Researchers used data previously collected from NASA's Hubble and Spitzer space telescopes and the European Space Agency's Herschel Space Telescope to analyze 304 developing stars, called protostars, in the Orion Complex, the nearest major star-forming region to Earth. (Spitzer and Herschel are no longer operational.)

In this largest-ever survey of nascent stars to date, researchers are finding that gas — clearing by a star's outflow may not be as important in determining its final mass as conventional theories suggest. The researchers' goal was to determine whether stellar outflows halt the infall of gas onto a star and stop it from growing.

Instead, they found that the cavities in the surrounding gas cloud sculpted by a forming star's outflow did not grow regularly as they matured, as theories propose.

"In one stellar formation model, if you start out with a small cavity, as the protostar rapidly becomes more evolved, its outflow creates an ever-larger cavity until the surrounding gas is eventually blown away, leaving an isolated star," explained lead researcher Nolan Habel of the University of Toledo in Ohio.

"Our observations indicate there is no progressive growth that we can find, so the cavities are not growing until they push out all of the mass in the cloud. So, there must be some other process going on that gets rid of the gas that doesn't end up in the star."

The team's results will appear in an upcoming issue of The Astrophysical Journal.

CREDITS:

NASA, ESA, and N. Habel and S. T. Megeath (University of Toledo)

How dark is the sky, and what does that tell us about the number of galaxies in the visible universe? Astronomers can estimate the total number of galaxies by counting everything visible in a Hubble deep field and then multiplying them by the total area of the sky. But other galaxies are too faint and distant to directly detect. Yet while we can’t count them, their light suffuses space with a feeble glow.

To measure that glow, astronomers have to escape the inner solar system and its light pollution, caused by sunlight reflecting off dust. A team of scientists has used observations by NASA’s New Horizons mission to Pluto and the Kuiper Belt to determine the brightness of this cosmic optical background. Their result sets an upper limit to the starlight emitted by faint, unresolved galaxies, showing that there is about twice as much optical light permeating space as can be accounted for by all known galaxies.

Credit: NASA/STScI

On March 14, NASA will join people across the U.S. as they celebrate an icon of nerd culture: the number pi. So well known and beloved is pi, also written π or 3.14, that it has a national holiday named in its honor. And it’s not just for mathematicians and rocket scientists. National Pi Day is widely celebrated among students, teachers, and science fans, too. Read on to find out what makes pi so special, how it’s used to explore space, and how you can join the celebration with resources from NASA.

2—How much pi do you need?

3—Officially official.

4—Pi helps us explore space!

5—Not just for rocket scientists.

6—Teachers rejoice.

7—How does NASA celebrate?

8—A pop-culture icon.

9—A numbers game.

10—Time to throw in the tau?

Black holes are mystifying yet terrifying cosmic phenomena. Unfortunately, people have a lot of ideas about them that are more science fiction than science. Black holes are not cosmic vacuum cleaners, sucking up anything and everything nearby. But there are a few ways Hollywood has vastly underestimated how absolutely horrid black holes really are.

Black holes are superdense objects with a gravitational pull so strong that not even light can escape them. Scientists have overwhelming evidence for two types of black holes, stellar and supermassive, and see hints of an in-between size that’s more elusive. A black hole’s type depends on its mass (a stellar black hole is five to 30 times the mass of the Sun, while a supermassive black hole is 100,000 to billions of times the mass of the Sun), and can determine where we’re most likely to find them and how they formed.

1. 100% Chance for Cosmic Winds

“Space weather” describes the changing conditions in space caused by stellar activity. Solar eruptions produce intense radiation and clouds of charged particles that sweep through our planetary system and can affect technology we rely on, damaging satellites and even causing electrical blackouts. Thankfully, Earth’s atmosphere and magnetic field protect us from most of the storms produced by the Sun.

2. Hello? Can You Still Hear Us?

We launched the Parker Solar Probe to learn more about the Sun. If you lived on a world around a supermassive black hole, you'd probably want to study it too. But it would be a lot more challenging!

You’d have to launch satellites that could withstand the extreme space weather. And then there would be major communication issues — a time-delay in messages sent between the spacecraft and your planet.

3. Can Someone Turn Off the Lights?

Supermassive black holes at the centers of galaxies typically have a lot of nearby stars. In fact, if you were to live on a planet near the center of the Milky Way, there would be so many stars you could read at night without using electricity.

4. Did Someone Leave the Oven On?

And not only would it be really bright, it would also be really toasty, thanks to radioactive heating! Those stars hanging around the black hole emit not just light but ghostly particles called neutrinos — speedy, tiny particles that weigh almost nothing and rarely interact with anything. While neutrinos coming from our Sun aren't enough to harm us, the volume that would be coming from the cluster of stars near a black hole would be enough to radioactively heat up whatever they slam into.

The planet would absorb neutrinos, which would, in turn, warm up the core of the planet eventually making it unbearably hot. It would be like living in a nuclear reactor. At least you’d be warm and could toss your winter coats?

5. You Are What You Eat?

If your planet got too close to a black hole, you’d likely face a gruesome fate. The forces from the black hole's gravity stretch matter, essentially turning it into a noodle. We call this spaghettification. (Beware the cosmic pasta-making machine?) Imagine yourself falling feet-first toward a black hole. Spaghettification happens because the gravity at your feet is sooooo much stronger than that at your head that you start to stretch out!

Credit: NASA

Light-year is the distance light travels in one year. Light zips through interstellar space at 186,000 miles (300,000 kilometers) per second and 5.88 trillion miles (9.46 trillion kilometers) per hour.

How far can light travel in one minute? 11,160,000 miles. It takes 43.2 minutes for sunlight to reach Jupiter, about 484 million miles away. Light is fast, but the distances are vast. In an hour, light can travel 671 million miles.

Earth is about eight light minutes from the Sun. A trip at light-speed to the very edge of our solar system – the farthest reaches of the Oort Cloud, a collection of dormant comets way, way out there – would take about 1.87 years. Keep going to Proxima Centauri, our nearest neighboring star, and plan on arriving in 4.25 years at light speed.

When we talk about the enormity of the cosmos, it’s easy to toss out big numbers – but far more difficult to wrap our minds around just how large, how far, and how numerous celestial bodies really are.

To get a better sense, for instance, of the true distances to exoplanets – planets around other stars – we might start with the theater in which we find them, the Milky Way galaxy

Our galaxy is a gravitationally bound collection of stars, swirling in a spiral through space. Based on the deepest images obtained so far, it’s one of about 2 trillion galaxies in the observable universe. Groups of them are bound into clusters of galaxies, and these into superclusters; the superclusters are arranged in immense sheets stretching across the universe, interspersed with dark voids and lending the whole a kind of spiderweb structure. Our galaxy probably contains 100 to 400 billion stars, and is about 100,000 light-years across. That sounds huge, and it is, at least until we start comparing it to other galaxies. Our neighboring Andromeda galaxy, for example, is some 220,000 light-years wide. Another galaxy, IC 1101, spans as much as 4 million light-years.

Based on observations by NASA’s Kepler Space Telescope, we can confidently predict that every star you see in the sky probably hosts at least one planet. Realistically, we’re most likely talking about multi-planet systems rather than just single planets. In our galaxy of hundreds of billions of stars, this pushes the number of planets potentially into the trillions. Confirmed exoplanet detections (made by Kepler and other telescopes, both in space and on the ground) now come to more than 4,000 – and that’s from looking at only tiny slices of our galaxy. Many of these are small, rocky worlds that might be at the right temperature for liquid water to pool on their surfaces.

The nearest-known exoplanet is a small, probably rocky planet orbiting Proxima Centauri – the next star over from Earth. A little more than four light-years away, or 24 trillion miles. If an airline offered a flight there by jet, it would take 5 million years. Not much is known about this world; its close orbit and the periodic flaring of its star lower its chances of being habitable.

The TRAPPIST-1 system is seven planets, all roughly in Earth’s size range, orbiting a red dwarf star about 40 light-years away. They are very likely rocky, with four in the “habitable zone” – the orbital distance allowing potential liquid water on the surface. And computer modeling shows some have a good chance of being watery – or icy – worlds. In the next few years, we might learn whether they have atmospheres or oceans, or even signs of habitability.

One of the most distant exoplanets known to us in the Milky Way is Kepler-443b. Traveling at light speed, it would take 3,000 years to get there. Or 28 billion years, going 60 mph.

Credit: NASA

Life and Death of a Planetary System

How did we get here? How do stars and planets come into being? What happens during a star's life, and what fate will its planets meet when it dies? Come along on this interstellar journey through time and scientific detective work.

It all begins with an unimaginably cold cloud. This cloud contains the seeds of whole new worlds – stars and planets about to be born.

Molecules of hydrogen and helium gas, which normally zip around at high speeds, slow down and clump together because of gravity. Tiny grains of silicates, iron and carbon-rich material — together classified simply as "dust" — send some of the gas’s energy back out into space, making the cloud even colder. The dust grains spiral into the central knot of matter, like water running down a drain.

The newborn star is a feisty baby, shooting out violent jets of magnetically accelerated material as it gets nourishment from the gas and dust whirling around it. Like a blob of pizza dough flattening out as a chef spins it, this material condenses into a flat disk. That "dough" has a preferred direction inherited from the collapse of the cloud. That same spin will remain with the system for its entire life, unless another star system gets close enough to interact with it.

A very young disk around a star contains mostly gas with dust -- no bigger than grains of sand -- swirling around in it. The baby star is still throwing out extremely hot winds, dominated by positively charged particles called protons and neutral helium atoms. A lot of the material from the disk is still falling on the star. But small groups of lucky dust particles are crashing into one another, clumping into larger objects. Planets will form from less than 1 percent of the mass of the disk.

Based on just an image of baby planets in a protoplanetary disk, it is impossible to determine what the system will look like as it matures.

At approximately 100 million to 1 billion years old, planets tend to settle down in their orbits and stars don’t flare up as much. Our own solar system, about 4.5 billion years old, is the model for this idea of planetary "middle age." Mandell thinks of our planetary system as about 45 to 50 years old, when scaled down to a human lifetime.

When our Sun approaches its red giant phase some 6 billion years from now, it will run out of fuel in its core. As hydrogen fusion slows, the core once again begins to contract. As the core gets smaller, it heats up until can kick off another round of nuclear reactions, fusing helium into heavier elements such as carbon, nitrogen and oxygen. The hotter core also makes hydrogen fuse in the “shell” of material surrounding the core. Meanwhile, extra heat produced deep within in the star causes its outer layer of gas to puff up.

When the core of the former red giant has exhausted all of its fuel and shed all the gas it can, the remaining dense stellar cinder is called a white dwarf. The white dwarf is considered “dead” because atoms inside of it no longer fuse to give the star energy. But it still “shines” because it is so hot. Eventually, it will cool off and fade from view. Our Sun will reach this death about 8 billion years from now.

Credit: NASA

Earth and the Moon are part of the universe, as are the other planets and their many dozens of moons. Along with asteroids and comets, the planets orbit the Sun. The Sun is one among hundreds of billions of stars in the Milky Way galaxy, and most of those stars have their own planets, known as exoplanets.

The Milky Way is but one of billions of galaxies in the observable universe — all of them, including our own, are thought to have supermassive black holes at their centers. All the stars in all the galaxies and all the other stuff that astronomers can’t even observe are all part of the universe. It is, simply, everything.

Though the universe may seem a strange place, it is not a distant one. Wherever you are right now, outer space is only 62 miles (100 kilometers) away. Day or night, whether you’re indoors or outdoors, asleep, eating lunch or dozing off in class, outer space is just a few dozen miles above your head. It’s below you too. About 8,000 miles (12,800 kilometers) below your feet — on the opposite side of Earth — lurks the unforgiving vacuum and radiation of outer space.

In fact, you’re technically in space right now. Humans say “out in space” as if it’s there and we’re here, as if Earth is separate from the rest of the universe. But Earth is a planet, and it’s in space and part of the universe just like the other planets. It just so happens that things live here and the environment near the surface of this particular planet is hospitable for life as we know it. Earth is a tiny, fragile exception in the cosmos. For humans and the other things living on our planet, practically the entire cosmos is a hostile and merciless environment.

Our planet, Earth, is an oasis not only in space, but in time. It may feel permanent, but the entire planet is a fleeting thing in the lifespan of the universe. For nearly two-thirds of the time since the universe began, Earth did not even exist. Nor will it last forever in its current state. Several billion years from now, the Sun will expand, swallowing Mercury and Venus, and filling Earth’s sky. It might even expand large enough to swallow Earth itself. It’s difficult to be certain. After all, humans have only just begun deciphering the cosmos.

While the distant future is difficult to accurately predict, the distant past is slightly less so. By studying the radioactive decay of isotopes on Earth and in asteroids, scientists have learned that our planet and the solar system formed around 4.6 billion years ago.

The universe, on the other hand, appears to be about 13.8 billion years old. Scientists arrived at that number by measuring the ages of the oldest stars and the rate at which the universe expands. They also measured the expansion by observing the Doppler shift in light from galaxies, almost all of which are traveling away from us and from each other. The farther the galaxies are, the faster they’re traveling away. One might expect gravity to slow the galaxies’ motion from one another, but instead they’re speeding up and scientists don’t know why. In the distant future, the galaxies will be so far away that their light will not be visible from Earth.

Put another way, the matter, energy and everything in the universe (including space itself) was more compact last Saturday than it is today.

Credit: NASA

A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity.

We live on a planet called Earth that is part of our solar system. But where is our solar system? It’s a small part of the Milky Way Galaxy.

A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle.

When you look up at stars in the night sky, you’re seeing other stars in the Milky Way. If it’s really dark, far away from lights from cities and houses, you can even see the dusty bands of the Milky Way stretch across the sky.

There are many galaxies besides ours, though. There are so many, we can’t even count them all yet! The Hubble Space Telescope looked at a small patch of space for 12 days and found 10,000 galaxies, of all sizes, shapes, and colors. Some scientists think there could be as many as one hundred billion galaxies in the universe.

Some galaxies are spiral-shaped like ours. They have curved arms that make it look like a pinwheel. Other galaxies are smooth and oval shaped. They’re called elliptical galaxies. And there are also galaxies that aren’t spirals or ovals. They have irregular shapes and look like blobs. The light that we see from each of these galaxies comes from the stars inside it.

Sometimes galaxies get too close and smash into each other. Our Milky Way galaxy will someday bump into Andromeda, our closest galactic neighbor. But don’t worry. It won’t happen for about five billion years. But even if it happened tomorrow, you might not notice. Galaxies are so big and spread out at the ends that even though galaxies bump into each other, the planets and solar systems often don’t get close to colliding.

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A meteor is a space rock—or meteoroid—that enters Earth's atmosphere. As the space rock falls toward Earth, the resistance—or drag—of the air on the rock makes it extremely hot. What we see is a "shooting star." That bright streak is not actually the rock, but rather the glowing hot air as the hot rock zips through the atmosphere.

When Earth encounters many meteoroids at once, we call it a meteor shower.

Why would Earth encounter many meteoroids at once? Well, comets, like Earth and the other planets, also orbit the sun. Unlike the nearly circular orbits of the planets, the orbits of comets are usually quite lop-sided.

As a comet gets closer to the sun, some of its icy surface boils off, releasing lots of particles of dust and rock. This comet debris gets strewn out along the comet's path, especially in the inner solar system (where we live) as the sun's heat boils off more and more ice and debris. Then, several times each year as Earth makes its journey around the sun, its orbit crosses the orbit of a comet, which means Earth smacks into a bunch of comet debris.

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Our Milky Way Galaxy is just one of billions of galaxies in the universe. Within it, there are at least 100 billion stars, and on average, each star has at least one planet orbiting it. This means there are potentially thousands of planetary systems like our solar system within the galaxy!

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The Sun—the heart of our solar system—is a yellow dwarf star, a hot ball of glowing gases.

Its gravity holds the solar system together, keeping everything from the biggest planets to the smallest particles of debris in its orbit. Electric currents in the Sun generate a magnetic field that is carried out through the solar system by the solar wind—a stream of electrically charged gas blowing outward from the Sun in all directions.

The connection and interactions between the Sun and Earth drive the seasons, ocean currents, weather, climate, radiation belts and aurorae. Though it is special to us, there are billions of stars like our Sun scattered across the Milky Way galaxy.

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Mars is the fourth planet from the Sun – a dusty, cold, desert world with a very thin atmosphere. Mars is also a dynamic planet with seasons, polar ice caps, canyons, extinct volcanoes, and evidence that it was even more active in the past.

Mars is one of the most explored bodies in our solar system, and it's the only planet where we've sent rovers to roam the alien landscape. Two NASA rovers and one lander are currently exploring the surface of Mars (and a Chinese lander is set to land later this year). An international fleet of eight orbiters are studying the Red Planet from above.

These robotic explorers have found lots of evidence that Mars was much wetter and warmer, with a thicker atmosphere, billions of years ago.

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The first planet found with the aid of a telescope, Uranus was discovered in 1781 by astronomer William Herschel, although he originally thought it was either a comet or a star.

It was two years later that the object was universally accepted as a new planet, in part because of observations by astronomer Johann Elert Bode. Herschel tried unsuccessfully to name his discovery Georgium Sidus after King George III. Instead the scientific community accepted Bode's suggestion to name it Uranus, the Greek god of the sky, as suggested by Bod

The seventh planet from the Sun with the third largest diameter in our solar system, Uranus is very cold and windy. The ice giant is surrounded by 13 faint rings and 27 small moons as it rotates at a nearly 90-degree angle from the plane of its orbit. This unique tilt makes Uranus appear to spin on its side, orbiting the Sun like a rolling ball.

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Our home planet is the third planet from the Sun, and the only place we know of so far that’s inhabited by living things.

While Earth is only the fifth largest planet in the solar system, it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal.

The name Earth is at least 1,000 years old. All of the planets, except for Earth, were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.”

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Saturn is the sixth planet from the Sun and the second largest planet in our solar system.

Adorned with thousands of beautiful ringlets, Saturn is unique among the planets. It is not the only planet to have rings—made of chunks of ice and rock—but none are as spectacular or as complicated as Saturn's.

Like fellow gas giant Jupiter, Saturn is a massive ball made mostly of hydrogen and helium.

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Similar in size and structure to Earth, Venus has been called Earth's twin. These are not identical twins, however – there are radical differences between the two worlds.

Venus has a thick, toxic atmosphere filled with carbon dioxide and it’s perpetually shrouded in thick, yellowish clouds of mostly sulfuric acid that trap heat, causing a runaway greenhouse effect. It’s the hottest planet in our solar system, even though Mercury is closer to the Sun. Venus has crushing air pressure at its surface – more than 90 times that of Earth – similar to the pressure you'd encounter a mile below the ocean on Earth.

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Jupiter has a long history surprising scientists—all the way back to 1610 when Galileo Galilei found the first moons beyond Earth. That discovery changed the way we see the universe.

Fifth in line from the Sun, Jupiter is, by far, the largest planet in the solar system – more than twice as massive as all the other planets combined.

Jupiter's familiar stripes and swirls are actually cold, windy clouds of ammonia and water, floating in an atmosphere of hydrogen and helium. Jupiter’s iconic Great Red Spot is a giant storm bigger than Earth that has raged for hundreds of years.

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The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth's Moon.

From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus, thanks to its dense atmosphere.

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There are many planetary systems like ours in the universe, with planets orbiting a host star. Our planetary system is named the "solar" system because our Sun is named Sol, after the Latin word for Sun, "solis," and anything related to the Sun we call "solar."

Our planetary system is located in an outer spiral arm of the Milky Way galaxy.

Our solar system consists of our star, the Sun, and everything bound to it by gravity — the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, dwarf planets such as Pluto, dozens of moons and millions of asteroids, comets and meteoroids. Beyond our own solar system, we have discovered thousands of planetary systems orbiting other stars in the Milky Way.

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