A Room With Earth Views! 🌎 Earlier This Week, Astronaut Ricky Arnold Captured This Spectacular View

Pi Guides the Way

It may be irrational but pi plays an important role in the everyday work of scientists at NASA. 

What Is Pi ?

Pi is the ratio of a circle’s circumference to its diameter. It is also an irrational number, meaning its decimal representation never ends and it never repeats. Pi has been calculated to more than one trillion digits, 

Why March 14?

March 14 marks the yearly celebration of the mathematical constant pi. More than just a number for mathematicians, pi has all sorts of applications in the real world, including on our missions. And as a holiday that encourages more than a little creativity – whether it’s making pi-themed pies or reciting from memory as many of the never-ending decimals of pi as possible (the record is 70,030 digits).

While 3.14 is often a precise enough approximation, hence the celebration occurring on March 14, or 3/14 (when written in standard U.S.  month/day format), the first known celebration occurred in 1988, and in 2009, the U.S. House of Representatives passed a resolution designating March 14 as Pi Day and encouraging teachers and students to celebrate the day with activities that teach students about pi.

5 Ways We Use Pi at NASA

Below are some ways scientists and engineers used pi.

Keeping Spacecraft Chugging Along

Propulsion engineers use pi to determine the volume and surface area of propellant tanks. It’s how they size tanks and determine liquid propellant volume to keep spacecraft going and making new discoveries. 

Getting New Perspectives on Saturn

A technique called pi transfer uses the gravity of Titan’s moon, Titan, to alter the orbit of the Cassini spacecraft so it can obtain different perspectives of the ringed planet.

Learning the Composition of Asteroids

Using pi and the asteroid’s mass, scientists can calculate the density of an asteroid and learn what it’s made of--ice, iron, rock, etc.

Measuring Craters

knowing the circumference, diameter and surface area of a crater can tell scientists a lot about the asteroid or meteor that may have carved it out.

Determining the Size of Exoplanets

Exoplanets are planets that orbit suns other than our own and scientists use pi to search for them. The first step is determining how much the light curve of a planet’s sun dims when a suspected planets passes in front of it.

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Tornado Recovery Underway at Michoud Assembly Facility

Teams at our Michoud Assembly Facility in New Orleans worked overnight and are continuing Wednesday with assessment and recovery efforts following a tornado strike at the facility Tuesday at 11:25 a.m. CST. All 3,500 employees at the facility have been accounted for, with five sustaining minor injuries.

Teams worked through the night on temporary repairs to secure the perimeter fencing and provide access for the essential personnel through the main gate. Approximately 40 to 50 percent of the buildings at Michoud have some kind of damage; about five buildings have some form of severe damage.

Approximately 200 parked cars were damaged, and there was damage to roads and other areas near Michoud.

“The entire NASA family pulls together during good times and bad, and the teams at the Michoud Assembly Facility are working diligently to recover from the severe weather that swept through New Orleans Tuesday and damaged the facility,” said acting NASA Administrator Robert Lightfoot. “We are thankful for the safety of all the NASA employees and workers of onsite tenant organizations, and we are inspired by the resilience of Michoud as we continue to assess the facility’s status.”

Teams will reassess the condition of the Vertical Assembly Center (VAC), as the initial examination revealed some electrical damage to its substation. The VAC is used to weld all major pieces of hardware for the core stage of the Space Launch System. The most recently welded part was removed from the facility last week.

The team has prioritized completing the assessment at the site’s main manufacturing building for the Space Launch System and Orion spacecraft flight hardware so power can be restored in phases and temporary protection put in place to shield hardware from any further inclement weather.

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Tournament Earth: The Earthly Eight

To celebrate Earth Observatory’s 20th anniversary and the 50th anniversary of Earth Day, we asked readers to pick our all-time best image. We have already completed two rounds of voting, which led to two rounds of stunning upsets. As we head into round 3, only two of the top eight seeds (#1s and #2s) remain. It is time now to cast your votes for the best of the Earthly 8. Voting ends on April 13 at 9 a.m. U.S. Eastern Time.

The nominees are separated into four groups: Past Winners, Home Planet, Land & Ice, and Sea & Sky. Check out the contenders still in the game:

Past Winners: Ocean Sand, Bahamas (#5 seed) vs. A View from Saturn (#2 seed)

Though the above image may resemble a new age painting straight out of an art gallery in Venice Beach, California, it is in fact a satellite image of the sands and seaweed in the Bahamas. The image was taken by the Enhanced Thematic Mapper plus (ETM+) instrument aboard the Landsat 7 satellite. Tides and ocean currents in the Bahamas sculpted the sand and seaweed beds into these multicolored, fluted patterns in much the same way that winds sculpted the vast sand dunes in the Sahara Desert.

This beautiful image of Saturn and its rings looks more like an artist’s creation than a real image, but in fact, the image is a composite (layered image) made from 165 images taken by the wide-angle camera on the Cassini spacecraft over nearly three hours on September 15, 2006. Scientists created the color in the image by digitally compositing ultraviolet, infrared, and clear-filter images and then adjusting the final image to resemble natural color. (A clear filter is one that allows in all the wavelengths of light the sensor is capable of detecting.) This image is a closeup view of the upper left quadrant of the rings, through which Earth is visible in the far, far distance. The full image can be seen here.

Home Planet: Twin Marbles (#1 seed) vs. Fire in the Sky and on the Ground (#7 seed)

A day’s clouds. The shape and texture of the land. The living ocean. City lights as a beacon of human presence across the globe. This amazingly beautiful view of Earth from space is a fusion of science and art, a showcase for the remote-sensing technology that makes such views possible, and a testament to the passion and creativity of the scientists who devote their careers to understanding how land, ocean, and atmosphere—even life itself—interact to generate Earth’s unique (as far as we know!) life-sustaining environment.

Astronauts on the International Space Station (ISS) used a digital camera to capture several hundred photographs of the aurora australis, or “southern lights,” while passing over the Indian Ocean on September 17, 2011. If you click on this movie, you can see the flowing ribbons and rays below as the ISS passed from south of Madagascar to just north of Australia between 17:22 and 17:45 Universal Time. Solar panels and other sections of the ISS fill some of the upper right side of the photograph.

Auroras are a spectacular sign that our planet is electrically and magnetically connected to the Sun. These light shows are provoked by energy from the Sun and fueled by electrically charged particles trapped in Earth’s magnetic field, or magnetosphere. In this case, the space around Earth was stirred up by an explosion of hot, ionized gas from the Sun—a coronal mass ejection—that left the Sun on September 14, 2011.

Ice and Land: Sand Dunes (#8 seed) vs. Retreat of Columbia Glacier (#6 seed)

Mountains of sand, some as tall as 300 meters (1000 feet), reach from the floor of Africa’s Namib Desert toward the sky. Driven by wind, these dunes march across the desert, bordered to the west by the Atlantic Ocean and in other directions by solid, rocky land.

The abrupt transition from sand to land is visible in this image, acquired on November 13, 2019, by the Operational Land Imager (OLI) on Landsat 8. They show the northern extent of the Namib Sand Sea—a field of sand dunes spanning more than 3 million hectares (more than 10,000 square miles) within the Namib-Naukluft Park, which was named a UNESCO World Heritage site in 2013. Sand appears red, painted by a layer of iron oxide.

Scientists have long studied Alaska's fast-moving Columbia Glacier, a tidewater glacier that descends through the Chugach Mountains into Prince William Sound. Yet the river of ice continues to deliver new surprises.

The image series begins in July 1986 (bottom image) with a false-color image captured by the Thematic Mapper (TM) sensor on the Landsat 5 satellite. The false-color image from July 2014 (top image), acquired by the Operational Land Imager on the Landsat 8 satellite, shows the extent of retreat after 28 years. Use the image comparison tool to better see the details.

Sea and Sky: Atafu Atoll, Tokelau (#8 seed) vs. Raikoke Erupts (#6 seed)

At roughly eight kilometers wide, Atafu Atoll is the smallest of three atolls and one island (Nukunonu and Fakaofo Atolls to the southeast and Swains Island to the south are not shown) comprising the Tokelau Islands group located in the southern Pacific Ocean. The primary settlement on Atafu is a village located at the northwestern corner of the atoll. The typical ring shape of the atoll is the result of coral reefs building up around a former volcanic island.

Unlike some of its perpetually active neighbors on the Kamchatka Peninsula, Raikoke Volcano on the Kuril Islands rarely erupts. The small, oval-shaped island most recently exploded in 1924 and in 1778.

The dormant period ended around 4:00 a.m. local time on June 22, 2019, when a vast plume of ash and volcanic gases shot up from its 700-meter-wide crater. Several satellites—as well as astronauts on the International Space Station—observed as a thick plume rose and then streamed east as it was pulled into the circulation of a storm in the North Pacific.

On the morning of June 22, astronauts shot this photograph of the volcanic plume rising in a narrow column and then spreading out in a part of the plume known as the umbrella region. That is the area where the density of the plume and the surrounding air equalize and the plume stops rising. The ring of clouds at the base of the column appears to be water vapor.

See all of the images and vote now HERE. 

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Whilst practicing solar distancing, Parker Solar Probe caught this rare glimpse of the twin tails on comet NEOWISE.☄

The twin tails are seen more clearly in this WISPR instrument processed image, which increased contrast and removed excess brightness from scattered sunlight, revealing more de-"tails". C/2020 F3 NEOWISE was discovered by our Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), on March 27. Since it's discovery the comet has been spotted by several NASA spacecraft, including Parker Solar Probe, NASA’s Solar and Terrestrial Relations Observatory, the ESA/NASA Solar and Heliospheric Observatory, and astronauts aboard the International Space Station.

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It's the International Day of Human Space Flight!

In this image, NASA astronaut Sunita Williams, Expedition 32 flight engineer, appears to touch the bright Sun during the mission's third spacewalk outside the International Space Station. Japan Aerospace Exploration Agency astronaut Aki Hoshide is visible in the reflection of Williams' helmet visor.

Today, April 12, is the International Day of Human Space Flight—marking Yuri Gagarin's first flight in 1961, and the first space shuttle launch in 1981.

As we honor global collaboration in exploration, we're moving forward to the Moon & Mars under the Artemis Accords.

Sign up to send your name around the Moon aboard Artemis I at go.nasa.gov/wearegoing.

People of OSIRIS-REx

As OSIRIS-REx closes in on its target destination—asteroid Bennu—anticipation is building for the first-ever, close-up glimpse of this small world. It took thousands of people to come this far. Get to know a few members of the team:

1. Carl Hergenrother, Astronomy Working Group Lead & Strategic and Tactical Scientist

Job Location: University of Arizona, Tucson Expertise: Asteroids & Comets Time on mission: Since before there was a mission Age: 45 Hometown: Oakland, New Jersey

“When you’re observing Bennu with a telescope, you see it as a dot. … So when it actually becomes its own little world, it’s really exciting—and almost a little sad. Up until that point, it can be anything. And now, there it is and that’s it.”

2. Heather Roper, Graphic Designer

Job Location: University of Arizona, Tucson Job Title: Graphic Designer Expertise: Visual Communications Time on mission: 5 years Age: 25 Hometown: Tucson, Arizona

“I really like the challenge of visually depicting the science of the mission and getting to show people things that we can’t see.”

3. Jason Dworkin, Project Scientist

Job Location: NASA’s Goddard Space Flight Center, Greenbelt, Maryland Expertise: Origin-of-life Chemistry Time on mission: Since before there was a mission Age: 49 Hometown: Houston, Texas

"In 10th grade, I had to do a science fair project for biology class. … I wanted to expand on chemistry experiments from old journal papers; but that could have been dangerous. I got in touch with … a pioneering scientist in origin-of-life research and asked for advice. He was worried that I would accidentally injure myself, so he invited me into his lab . . . that helped set my career.”

4. Sara Balram Knutson, Science Operations Lead Engineer

Job Location: University of Arizona, Tucson Expertise: Aerospace Engineering Time on mission: 6 years Age: 31 Hometown: Vacaville, California

“My dad was in the Air Force, so I grew up being a bit of an airplane nerd. When I was in high school, I really liked math, science, and anything having to do with flight. I looked for a field where I could combine all those interests and I found aerospace engineering.”

5. Nancy Neal Jones, Public Affairs Lead

Job Location: NASA’s Goddard Space Flight Center, Greenbelt, Maryland Expertise: Science Communications Time on mission: 7 years Age: 51 Hometown: New York, New York

“We’re going to a pristine asteroid to take a sample to bring to Earth. This means that my children and grandchildren, if they decide to go into the sciences, may have an opportunity analyze the Bennu samples.”

6. Javier Cerna, Communications System Engineer

Job Location: Lockheed Martin Corporation, Littleton, Colorado Expertise: Electrical Engineering Time on mission: Since before there was a mission Age: 37 Hometown: Born in Mexico City, and raised in Los Angeles, and Las Cruces, New Mexico

“One thing we do is evaluate how strong the signal from the spacecraft is—kind of like checking the strength of the WiFi connection. Basically, we’re ensuring that the link from the spacecraft to the ground, and vice versa, stays strong.”

7. Jamie Moore, Contamination Control Engineer

Job Location: Lockheed Martin Corporation, Littleton, Colorado Expertise: Chemistry Time on mission: 5 years Age: 32 Hometown: Apple Valley, Minnesota & Orlando, Florida

“I was there for just about every deployment of the sampling hardware to make sure it was kept clean and to evaluate the tools engineers were using. I even went to Florida with the spacecraft to make sure it stayed clean until launch.”

8. Mike Moreau, Flight Dynamics System Manager

Job Location: NASA’s Goddard Space Flight Center, Greenbelt, Maryland; Littleton, Colorado Expertise: Mechanical and aerospace engineering Time on mission: 5 years Age: 47 Hometown: Swanton, Vermont

“I grew up on a dairy farm in Vermont, which is a world away from working for NASA. But I can trace a lot of my success as an engineer and a leader back to things that I learned on my dad’s farm.”

9. Johnna L. McDaniel, Contamination Control Specialist

Job Location: NASA’s Kennedy Space Center, Florida Expertise: Anti-Contamination Cleaning Time on Mission: 4 months Age: 53 Hometown: Cocoa, Florida

“The clothing requirements depend on the payload. With OSIRIS-Rex, we could not wear any items made with nylon. This was because they have amino acid-based polymers in them and would have contaminated the spacecraft. I even had a special bucket for mopping.”

10. Annie Hasten, Senior Financial Analyst

Job Location: Lockheed Martin Corporation, Steamboat Springs, Colorado Expertise: Business Time on Mission: 1.5 years Age: 30 Hometown: Littleton, Colorado

“I think it’s a pleasure to work with people who are so intensely passionate about their jobs. These engineers are doing their dream jobs, so you feed off of that positive energy.”

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25 Years of Exploring the Universe with NASA's Chandra Xray Observatory

Illustration of the Chandra telescope in orbit around Earth. Credit: NASA/CXC & J. Vaughan

On July 23, 1999, the space shuttle Columbia launched into orbit carrying NASA’s Chandra X-ray Observatory. August 26 marked 25 years since Chandra released its first images.

These were the first of more than 25,000 observations Chandra has taken. This year, as NASA celebrates the 25th anniversary of this telescope and the incredible data it has provided, we’re taking a peek at some of its most memorable moments.

About the Spacecraft

The Chandra telescope system uses four specialized mirrors to observe X-ray emissions across the universe. X-rays that strike a “regular” mirror head on will be absorbed, so Chandra’s mirrors are shaped like barrels and precisely constructed. The rest of the spacecraft system provides the support structure and environment necessary for the telescope and the science instruments to work as an observatory. To provide motion to the observatory, Chandra has two different sets of thrusters. To control the temperatures of critical components, Chandra's thermal control system consists of a cooling radiator, insulators, heaters, and thermostats. Chandra's electrical power comes from its solar arrays.

Learn more about the spacecraft's components that were developed and tested at NASA’s Marshall Space Flight Center in Huntsville, Alabama. Fun fact: If the state of Colorado were as smooth as the surface of the Chandra X-ray Observatory mirrors, Pike's Peak would be less than an inch tall.

Engineers in the X-ray Calibration Facility at NASA’s Marshall Space Flight Center in Huntsville, Alabama, integrating the Chandra X-ray Observatory’s High-Resolution Camera with the mirror assembly, in this photo taken March 16, 1997. Credit: NASA

Launch

When space shuttle Columbia launched on July 23, 1999, Chandra was the heaviest and largest payload ever launched by the shuttle. Under the command of Col. Eileen Collins, Columbia lifted off the launch pad at NASA’s Kennedy Space Center in Florida. Chandra was deployed on the mission’s first day.

Reflected in the waters, space shuttle Columbia rockets into the night sky from Launch Pad 39-B on mission STS-93 from Kennedy Space Center. Credit: NASA

First Light Images

Just 34 days after launch, extraordinary first images from our Chandra X-ray Observatory were released. The image of supernova remnant Cassiopeia A traces the aftermath of a gigantic stellar explosion in such captivating detail that scientists can see evidence of what is likely the neutron star.

“We see the collision of the debris from the exploded star with the matter around it, we see shock waves rushing into interstellar space at millions of miles per hour,” said Harvey Tananbaum, founding Director of the Chandra X-ray Center at the Smithsonian Astrophysical Observatory.

Cassiopeia A is the remnant of a star that exploded about 300 years ago. The X-ray image shows an expanding shell of hot gas produced by the explosion colored in bright orange and yellows. Credit: NASA/CXC/SAO

A New Look at the Universe

NASA released 25 never-before-seen views to celebrate the telescopes 25th anniversary. This collection contains different types of objects in space and includes a new look at Cassiopeia A. Here the supernova remnant is seen with a quarter-century worth of Chandra observations (blue) plus recent views from NASA’s James Webb Space Telescope (grey and gold).

This image features deep data of the Cassiopeia A supernova, an expanding ball of matter and energy ejected from an exploding star in blues, greys and golds. The Cassiopeia A supernova remnant has been observed for over 2 million seconds since the start of Chandra’s mission in 1999 and has also recently been viewed by the James Webb Space Telescope. Credit: NASA/CXC/SAO

Can You Hear Me Now?

In 2020, experts at the Chandra X-ray Center/Smithsonian Astrophysical Observatory (SAO) and SYSTEM Sounds began the first ongoing, sustained effort at NASA to “sonify” (turn into sound) astronomical data. Data from NASA observatories such as Chandra, the Hubble Space Telescope, and the James Webb Space Telescope, has been translated into frequencies that can be heard by the human ear.

SAO Research shows that sonifications help many types of learners – especially those who are low-vision or blind -- engage with and enjoy astronomical data more.

Click to watch the “Listen to the Universe” documentary on NASA+ that explores our sonification work: Listen to the Universe | NASA+

An image of the striking croissant-shaped planetary nebula called the Cat’s Eye, with data from the Chandra X-ray Observatory and Hubble Space Telescope.  NASA’s Data sonification from Chandra, Hubble and/or Webb telecopes allows us to hear data of cosmic objects. Credit: NASA/CXO/SAO

Celebrate With Us!

Dedicated teams of engineers, designers, test technicians, and analysts at Marshall Space Flight Center in Huntsville, Alabama, are celebrating with partners at the Chandra X-ray Center and elsewhere outside and across the agency for the 25th anniversary of the Chandra X-ray Observatory. Their hard work keeps the spacecraft flying, enabling Chandra’s ongoing studies of black holes, supernovae, dark matter, and more.

Chandra will continue its mission to deepen our understanding of the origin and evolution of the cosmos, helping all of us explore the Universe.

The Chandra Xray Observatory, the longest cargo ever carried to space aboard the space shuttle, is shown in Columbia’s payload bay. This photo of the payload bay with its doors open was taken just before Chandra was tilted upward for release and deployed on July 23, 1999. Credit: NASA

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Solar System: Things to Know This Week

Here are a few things you should know about our solar system this week:

1. Gearing Up for a Grand Finale

There’s just a year left until the Cassini mission begins its Grand Finale – the final phase of its mission, during which the spacecraft will dive repeatedly between the planet and the rings. To get ready, the Cassini team has launched an enhanced, mobile device-friendly version of the mission website. The site includes information about Cassini, Saturn, the moons and the rings – but it also tells the human stories behind one of the most ambitions expeditions of all time.

2.Caught in Transit

On Monday, May 9, the planet Mercury will cross directly in front of the sun, an event that hasn’t occurred since 2006 and won’t happen again until 2019. Find out how to watch HERE.  

3. A Moon for Makemake

Our Hubble Space Telescope has spotted a small, dark moon orbiting Makemake (pronounced “MAH-kay MAH-kay). Make make is the second brightest icy dwarf planet – after Pluto – in the faraway Kuiper Belt.

4. The Age of the Aquarids

The Eta Aquarid meteor shower is the first of two showers that occur each year as a result of Earth passing through dust released by Halley’s Comet. This year, it should peak on the night of May 5/6. Get tips for watching HERE.

5. The Southern Lights of Saturn

On May 4, Cassini will reach periapse, the closest point to Saturn in the spacecraft’s orbit. At about this time, Cassini’s cameras will monitor Saturn’s south polar aurorae, and also image the bright limb of the planet to better understand its upper haze layers.

Want to learn more? Read our full list of the 10 things to know this week about the solar system HERE.

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The Artemis Story: Where We Are Now and Where We’re Going

Using a sustainable architecture and sophisticated hardware unlike any other, the first woman and the next man will set foot on the surface of the Moon by 2024. Artemis I, the first mission of our powerful Space Launch System (SLS) rocket and Orion spacecraft, is an important step in reaching that goal.

As we close out 2019 and look forward to 2020, here’s where we stand in the Artemis story — and what to expect in 2020. 

Cranking Up The Heat on Orion

The Artemis I Orion spacecraft arrived at our Plum Brook Station in Sandusky, Ohio, on Tuesday, Nov. 26 for in-space environmental testing in preparation for Artemis I.

This four-month test campaign will subject the spacecraft, consisting of its crew module and European-built service module, to the vacuum, extreme temperatures (ranging from -250° to 300° F) and electromagnetic environment it will experience during the three-week journey around the Moon and back. The goal of testing is to confirm the spacecraft’s components and systems work properly under in-space conditions, while gathering data to ensure the spacecraft is fit for all subsequent Artemis missions to the Moon and beyond. This is the final critical step before the spacecraft is ready to be joined with the Space Launch System rocket for this first test flight in 2020!

Bringing Everyone Together

On Dec. 9, we welcomed members of the public to our Michoud Assembly Facility in New Orleans for #Artemis Day and to get an up-close look at the hardware that will help power our Artemis missions. The 43-acre facility has more than enough room for guests and the Artemis I, II, and III rocket hardware! NASA Administrator Jim Bridenstine formally unveiled the fully assembled core stage of our SLS rocket for the first Artemis mission to the Moon, then guests toured of the facility to see flight hardware for Artemis II and III. The full-day event — complete with two panel discussions and an exhibit hall — marked a milestone moment as we prepare for an exciting next phase in 2020.

Rolling On and Moving Out

Once engineers and technicians at Michoud complete functional testing on the Artemis I core stage, it will be rolled out of the Michoud factory and loaded onto our Pegasus barge for a very special delivery indeed. About this time last year, our Pegasus barge crew was delivering a test version of the liquid hydrogen tank from Michoud to NASA’s Marshall Space Flight Center in Huntsville for structural testing. This season, the Pegasus team will be transporting a much larger piece of hardware — the entire core stage — on a slightly shorter journey to the agency’s nearby Stennis Space Center near Bay St. Louis, Mississippi.

Special Delivery

Why Stennis, you ask? The giant core stage will be locked and loaded into the B2 Test Stand there for the landmark Green Run test series. During the test series, the entire stage, including its extensive avionics and flight software systems, will be tested in full. The series will culminate with a hot fire of all four RS-25 engines and will certify the complex stage “go for launch.” The next time the core stage and its four engines fire as one will be on the launchpad at NASA’s Kennedy Space Center in Florida.

Already Working on Artemis II

As Orion and SLS make progress toward the pad for Artemis I, employees at NASA centers and large and small companies across America are hard at work assembling and manufacturing flight hardware for Artemis II and beyond.  The second mission of SLS and Orion will be a test flight with astronauts aboard that will go around the Moon before returning home. Our work today will pave the way for a new generation of moonwalkers and Artemis explorers.

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It’s International Asteroid Day!

There are more than 700,000 known asteroids, but how much do you know about these rocky remnants left over from the birth of our solar system 4.6 billion years ago? 

Today, June 30 is International Asteroid Day. Here are some things to know about our fascinating space rubble.

1. A Place in Space 

Asteroids—named by British astronomer William Herschel from the Greek expression meaning "star-like"—are rocky, airless worlds that are too small to be called planets. But what they might lack in size they certainly make up for in number: An estimated 1.1 to 1.9 million asteroids larger than 1 kilometer are in the Main Belt between the orbits of Mars and Jupiter. And there are millions more that are smaller in size. Asteroids range in size from Vesta—the largest at about 329 miles (529 kilometers) wide—to bodies that are just a few feet across.

2. What Lies Beneath 

Asteroids are generally categorized into three types: carbon-rich, silicate, or metallic, or some combination of the three. Why the different types? It all comes down to how far from the sun they formed. Some experienced high temperatures and partly melted, with iron sinking to the center and volcanic lava forced to the surface. The asteroid Vesta is one example we know of today.

3. Small Overall 

If all of the asteroids were combined into a ball, they would still be much smaller than the Earth's moon.

4. Except for a Big One

In 1801, Giuseppe Piazzi discovered the first and then-largest asteroid, Ceres, orbiting between Mars and Jupiter. Ceres is so large that it encompasses about one-fourth of the estimated total mass of all the asteroids in the asteroid belt. In 2006, its classification changed from asteroid to  as a dwarf planet.

5. Mission to a Metal World 

NASA's Psyche mission will launch in 2022 to explore an all-metal asteroid—what could be the core of an early planet—for the very first time. And in October 2021, the Lucy mission will be the first to visit Jupiter's swarms of Trojan asteroids.

6. Near-Earth Asteroids

The term 'near' in near-Earth asteroid is actually a misnomer; most of these bodies do not come close to Earth at all. By definition, a near-Earth asteroid is an asteroid that comes within 28 million miles (44 million km) of Earth's orbit. As of June 19, 2017, there are 16,209 known near-Earth asteroids, with 1,803 classified as potentially hazardous asteroids (those that could someday pose a threat to Earth).

7. Comin' in Hot 

About once a year, a car-sized asteroid hits Earth's atmosphere, creates an impressive fireball, and burns up before reaching the surface.

8. But We're Keeping an Eye Out

Ground-based observatories and facilities such as Pan-STARRS, the Catalina Sky Survey, and ATLAS are constantly on the hunt to detect near-Earth asteroids. NASA also has a small infrared observatory in orbit about the Earth: NEOWISE. In addition to detecting asteroids and comets, NEOWISE also characterizes these small bodies.

9. Buddy System

Roughly one-sixth of the asteroid population have a small companion moon (some even have two moons). The first discovery of an asteroid-moon system was of asteroid Ida and its moon Dactyl in 1993.

10. Earthly Visitors 

Several NASA space missions have flown to and observed asteroids. The NEAR Shoemaker mission landed on asteroid Eros in 2001 and NASA's Dawn mission was the first mission to orbit an asteroid in 2011. In 2005, the Japanese spacecraft Hayabusa landed on asteroid Itokawa. Currently, NASA's OSIRIS-REx is en route to a near-Earth asteroid called Bennu; it will bring a small sample back to Earth for study.

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