Why Do Scientists Think There Could Have Been Life On Mars?

Countdown to Launch of Landsat 9

We’re launching Landsat 9 — the ninth in a series of satellite missions from NASA and the U.S. Geological Survey (USGS) that have been collecting images of our planet for almost 50 years. Follow along as we count down to launch!

A normal launch countdown starts at 10, but for Landsat 9, we’re jumping in with L-9!

There are 9 million images in the USGS/NASA Landsat archive! They’re all available for free, for use by scientists, data managers, and anyone else who’s interested. You can even download them!

Landsat 9 won’t be orbiting alone. Working together, Landsat 9 and Landsat 8 will completely image Earth every 8 days! This helps us track changes on the planet’s surface as they happen in near-real-time.

Landsat sees all 7 continents! From Antarctic ice to growing cities to changing forests, Landsat measures land — and coastal regions — all around the globe.

Working in space is really hard. Landsat 6 never made it to orbit, an important reminder that failures can be opportunities to learn and grow. Shortly after the unsuccessful launch, engineers got to work on Landsat 7, which is still collecting data today — 22 years later.

We have 5 decades of Landsat observations, the longest continuous record of Earth’s land surfaces in existence! While building the original Landsat in the 1970s, it would have been hard to imagine that this mission would still be providing crucial data about our planet today.

For each color band collected, Landsat 9 will see 4 times the shades of light as the previous Landsat mission! With more than 16,000 different intensities detected, Landsat 9 will be able to see crucial details on our planet’s surface.

Our eyes detect 3 colors of light: red, green, and blue — and Landsat does too! But Landsat 9 also detects wavelengths that can be combined to measure things our eyes can’t, like crop stress, coral reef health, fires, and more.

There are 2 instruments on Landsat 9! The Operational Land Imager 2 collects light, and works kind of like our eyes — or cameras — to make data-rich images. The Thermal Infrared Sensor 2 measures temperature, helping monitor plant health, fires, and more.

The Landsat program is the result of 1 amazing partnership! For more than 50 years, we’ve worked with the U.S. Geological Survey to design, build, launch, and manage Landsat satellites.

Two agencies working together makes for the longest continuous record of Earth’s surfaces. Now, let’s launch this satellite!

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Seeing Saharan Dust from Space

Last year, Godzilla made its way across the Atlantic Ocean. No, it wasn’t a giant lizard monster, but a cloud of dust so large it could be seen from a million miles away in space.

The plume of dust blowing from the Sahara Desert broke records and was nicknamed the “Godzilla plume.”

This year, another massive dust plume is traveling across the Atlantic.

The transport of dust from the Sahara to the Americas isn’t unusual: every year, winds pick up more than 180 million tons of dust particles from the Sahara Desert, move them over the African continent and carry them all the way across the Atlantic Ocean, depositing much of the dust along the way.

What’s remarkable about the past two years is the size of the plumes. Last year, the “Godzilla plume” was the largest dust storm in our two decades of observations.

Although this year’s plume has yet to complete its journey across the Atlantic, dust plumes from the Sahara often have important impacts on the Americas.

So, why do the dust plumes matter?

Before the Sahara was a desert, it was a lakebed, where nutrients like phosphorous and iron were deposited before the lake dried up. As a result, winds pick up these nutrients in the dust plumes. Some of these nutrients get deposited in the Atlantic Ocean, feeding marine life – iron, for example, is critical for marine life. Phosphorus is also a much-needed nutrient that fertilizes vegetation in the Amazon rainforest. The amount of phosphorus deposited by Saharan dust plumes into the Amazon every year – around 22,000 tons – is roughly equivalent to the amount that gets removed from the rainforest’s soil by weather conditions. In other words, long term, the dust plumes provide an essential nutrient to the Amazon’s vegetation.

Both the dust plumes themselves and the conditions associated with them can also influence the formation of tropical storms during hurricane season. As climate change appears to be strengthening the strongest storms, understanding the relationship between dust plumes and hurricanes has only grown more important.

The dust plumes can carry microbes that can be deadly and can worsen air quality, creating potentially dangerous conditions for sensitive populations. The iron in the plumes can also kick off blooms of toxic algae off the coast of Florida that result from the increase in nutrients in the ocean.

What comes next for Saharan dust? We’re still looking into it!

Some research suggests dust plumes will intensify with higher temperatures and dryer conditions, creating more loose dust to be picked up. However, other research shows that rising ocean temperatures and changing wind speeds would result in more rainfall and vegetation in the desert, reducing how much dust blows across the Atlantic. Make sure to follow us on Tumblr for your regular dose of space!

Studying Sediments in Space

An International Space Station investigation called BCAT-CS studies dynamic forces between sediment particles that cluster together.

For the study, scientists sent mixtures of quartz and clay particles to the space station and subjected them to various levels of simulated gravity.

Conducting the experiment in microgravity makes it possible to separate out different forces that act on sediments and look at the function of each.

Sediment systems of quartz and clay occur many places on Earth, including rivers, lakes, and oceans, and affect many activities, from deep-sea hydrocarbon drilling to carbon sequestration.

Understanding how sediments behave has a range of applications on Earth, including predicting and mitigating erosion, improving water treatment, modeling the carbon cycle, sequestering contaminants and more accurately finding deep sea oil reservoirs.

It also may provide insight for future studies of the geology of new and unexplored planets.

Follow @ISS_RESEARCH to learn more.

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Spinoffs: Space Station Innovations in Your Cart (and Heart!)

You might think NASA technology is just spaceships and telescopes, but did you know the camera in your cell phone is, too? It’s one of many NASA innovations now found everywhere on Earth.

The International Space Station has had crew living on it for 25 years straight. In that time, the space station has enabled a tremendous amount of research, helping NASA and scientists better understand long-term living in space – but it’s not just knowledge coming back down to Earth! Technologies developed for the space station and experiments conducted aboard the orbiting lab also benefit people on the planet below. Here are a few of these inventions, or spinoffs, you can find in your everyday life.

A Sunscreen That Blocks Radiation in Space – and on Your Face

After surviving for 18 months outside the International Space Station, an extremely hardy organism is now improving sunscreens and face cream products from a cosmetics company, which licensed use of the organism from NASA’s Jet Propulsion Laboratory.

Build Muscle With or Without Gravity

Muscles atrophy quickly in space, so when astronauts began long stays on the International Space Station, they needed some specialized exercise equipment. A resistance mechanism made of a coiled metal spring formed the basis of the first way for astronauts to “lift weights” in space. Soon after, that same design became the heart of compact home gym equipment.

Fresh Greens Every Day of the Year

The need to grow fresh food in space pushed NASA to develop indoor agriculture techniques. Thanks to the agency’s research, private companies are building on NASA’s vertical farm structure, plant-growth “recipes,” and environmental-control data to create indoor farms, resulting in higher crop yields and better-quality produce while conserving water and energy and eliminating the need for pesticides.

Cultivating Hearts and Knees in Space

Gravity is a significant obstacle to bioprinting cells and growing human tissue on Earth because heavier components settle to the bottoms of petri dishes. In the absence of gravity, each cell layer stays in place, which is how it’s possible to grow heart and knee tissue on the space station. The same principle also allows mixing of complex pharmaceuticals on orbit.

Storing Oodles of Energy

NASA chose nickel-hydrogen batteries to power the Hubble Space Telescope and the International Space Station because the technology is safe, reliable in extreme temperatures, and long-lived. NASA’s improvements brought down the cost of the technology, which is now used by large-scale utilities and renewable power plants that need to store energy generated by intermittent sources.

You can read about many more products sourced from the ISS on spinoff.nasa.gov.

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Weird and Wonderful Irregular Galaxies

Spiral and elliptical galaxies seem neatly put together, but what happened to irregular galaxies? Irregular galaxies have one-of-a-kind shapes and many look like blobs! Why do they look the way they do? Astronomers think the uniqueness of these galaxies results from their interactions with other galaxies — like when they pass close to one another or even collide!

Looking back at the early universe with the help of our Hubble Space Telescope’s “deep field” observations, astronomers can peek at galaxies millions and billions of light-years away. They noticed that these far-away galaxies appear unusually messy, showing more star formation and mergers than galaxies closer to the Milky Way.

We also see irregular galaxies closer to home, though. Some may form when two galaxies pass close together in a near-miss. When this happens, their gravity pulls stars out of place in both galaxies, messing up the neat structure they originally had as spiral or elliptical galaxies. Think of it like this: you happen to have a pile of papers sitting at the edge of a table and when someone passes close by the papers become ruffled and may scatter everywhere! Even though the two galaxies never touched, gravity's effects leave them looking smeared or distorted.

Some irregular galaxies result from the collision between two galaxies. And while some of these look like a blob of stars and dust, others form dazzling ring galaxies! Scientists think these may be a product of collisions between small and large galaxies. These collisions cause ripples that disturb both galaxies, throwing dust, gas, and stars outward. When this happens, it pushes out a ring of material, causing gas clouds to collide and spark the birth of new stars. After just a few million years, stars larger than our Sun explode as supernovae, leaving neutron stars and black holes throughout the ring!

Not all galaxy collisions create irregular galaxies — our Milky Way spiral galaxy has gone through many mergers but has stayed intact! And for some interacting galaxies, being an irregular galaxy may just be a phase in their transformation. We’re observing them at a snapshot in time where things are messy, but they may eventually become neat and structured spirals and ellipticals.

Irregular galaxies are similar to each other, but unique and beautiful because of their different interactions, whether they’re just passing another galaxy or taking part in a dramatic collision. Keep up with NASA Universe on Facebook and Twitter where we post regularly about galaxies.

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What’s Up November 2017

What’s Up For November?

Dawn pairing of Jupiter and Venus, Moon shines near star clusters, meteor activity all month long!

This month binoculars will come in handy--to view the moon, star clusters, and a close pairing of Venus and Jupiter.

You can’t miss bright Venus in the predawn sky. This month Venus pairs up with Jupiter on the morning of November 13th.

The Leonids peak on a moonless November 17th. Expect no more than 10 meteors an hour around 3:00 a.m., the height of the shower.

The Northern and Southern sub-branches of the Taurid meteor shower offer sparse counts of about 5 meteors per hour, but slow, bright meteors are common.

The nearby November Orionids peak on the 28th. In contrast to the Taurids, the Orionids are swift. But don’t expect more than 3 meteors per hour.

The moon glides by three beautiful star clusters in the morning sky this month, and a pair of binoculars will allow you to see the individual stars in the clusters. Aim your binoculars at the Pleiades and the moon on the 5th.

Then aim at the Messier or M-35 cluster and the moon on the 7th and the Beehive cluster and the moon on the 10th.

Meanwhile, at dusk, catch Saturn as it dips closer to the western horizon and pairs up with Mercury on the 24th through the 28th.

Also, Comet C/2017 O1 should still be a binocular-friendly magnitude 7 or 8 greenish object in November. Use Polaris, the North Star as a guide. Look in the East to Northeast sky in the late evening.  

Watch the full What’s Up for November Video: 

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Ever wanted to ask a NASA astronaut a question? Here’s your chance!

NASA astronaut Kate Rubins will be taking your questions in an Answer Time session on Thursday, October 17 from 12pm - 1pm ET here on NASA’s Tumblr! Find out what it’s like to live and work 254 miles above our planet’s surface. Make sure to ask your question now by visiting http://nasa.tumblr.com/ask!

Dr. Kate Rubins was selected in 2009 as one of nine members of the 20th NASA astronaut class. She holds a Bachelor of Science degree in Molecular Biology and a Ph.D. in Cancer Biology. During her first spaceflight from July - October 2016 as a member of the Expedition 49 and 50 crew, Dr. Rubins made history by becoming the first person to sequence DNA in space. She also worked on the Heart Cells Experiment which studied how heart muscle tissues contract, grow and change in microgravity. Before becoming a NASA astronaut, Dr. Rubins worked with some of the world’s most dangerous pathogens, heading 14 researchers studying viral diseases that primarily affect Central and West Africa. 

Dr. Kate Rubins Fun Facts

Dr. Rubins and colleagues developed the first model of smallpox infection.

She conducted her undergraduate research on HIV-1 integration in the Infectious Diseases Laboratory at the Salk Institute for Biological Studies. 

She conducted research on filoviruses (Ebola and Marburg), Arenaviruses (Lassa Fever) and collaborative projects with the U.S. Army to develop therapies for Ebola and Lassa viruses. 

She has logged 115 days in space and 12 hours and 46 minutes of spacewalk time.

She enjoys running, cycling, swimming, flying, scuba diving and reading. 

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Our Roman Space Telescope’s Dish is Complete!

NASA engineers recently completed tests of the high-gain antenna for our Nancy Grace Roman Space Telescope. This observatory has some truly stellar plans once it launches by May 2027. Roman will help unravel the secrets of dark energy and dark matter – two invisible components that helped shape our universe and may determine its ultimate fate. The mission will also search for and image planets outside our solar system and explore all kinds of other cosmic topics.

However, it wouldn’t be able to send any of the data it will gather back to Earth without its antenna. Pictured above in a test chamber, this dish will provide the primary communication link between the Roman spacecraft and the ground. It will downlink the highest data volume of any NASA astrophysics mission so far.

The antenna reflector is made of a carbon composite material that weighs very little but will still withstand wide temperature fluctuations. It’s very hot and cold in space – Roman will experience a temperature range of minus 26 to 284 degrees Fahrenheit (minus 32 to 140 degrees Celsius)!

The dish spans 5.6 feet (1.7 meters) in diameter, standing about as tall as a refrigerator, yet only weighs 24 pounds (10.9 kilograms) – about as much as a dachshund. Its large size will help Roman send radio signals across a million miles of intervening space to Earth.

At one frequency, the dual-band antenna will receive commands and send back information about the spacecraft’s health and location. It will use another frequency to transmit a flood of data at up to 500 megabits per second to ground stations on Earth. The dish is designed to point extremely accurately at Earth, all while both Earth and the spacecraft are moving through space.

Engineers tested the antenna to make sure it will withstand the spacecraft’s launch and operate as expected in the extreme environment of space. The team also measured the antenna’s performance in a radio-frequency anechoic test chamber. Every surface in the test chamber is covered in pyramidal foam pieces that minimize interfering reflections during testing. Next, the team will attach the antenna to the articulating boom assembly, and then electrically integrate it with Roman’s Radio Frequency Communications System.

Learn more about the exciting science this mission will investigate on Twitter and Facebook.

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Get Space-Crafty with Earth Science!

It’s time to get space-crafty! (Get it?) We’re getting ready to launch Landsat 9 into space this fall, and we want to know, how does Landsat inspire you?

For nearly 50 years, Landsat satellites have been collecting important data and taking beautiful images of Earth, as a partnership between NASA and the U.S. Geological Survey. Scientists and policy makers alike use this data to understand climate change, deforestation, the growth of cities, and so much more.

In celebration of the Landsat 9 launch in September, we are calling all crafters to create space-crafts inspired by your favorite Landsat image! From watercolor paintings to needlework to frosted cakes, let your creativity flow and show us how you see Landsat images.

Post a picture of your craft on Instagram, Twitter or Facebook with the hashtag #LandsatCraft. We will spotlight some on social media!

For a little inspiration, here are some #LandsatCraft examples from some of the people who work with Landsat:

“Looking through the Visible Earth Landsat gallery for inspiration, I saw the Landsat Image Mosaic of Antarctica (LIMA) and knew immediately what I had to do -- recreate it in a mosaic of my own. LIMA is a composite of more than 1,000 cloud-free Landsat 7 images of Antarctica, and when it was released in 2007 it was our first high resolution, true-color look at the icy continent.” – Kate Ramsayer, NASA Landsat Communications Coordinator

“I love embroidering satellite imagery and NASA data. For Landsat, I wanted something with lots of straight lines -- much easier to stitch! -- and crop fields like these fit the bill. It’s amazing how clearly we can see the influence of human activities in satellite imagery like this. It’s a constant reminder of the effect we have on our home planet.” – Katy Mersmann, Earth Science Social Media Lead

“We didn’t have the discipline or the organizational skills to do any of the really, really fancy images, like Lena Delta, so we chose Garden City, Kansas in 1972. We added a model of Landsat 1, too.” – Ryan Fitzgibbons, Earth Science Producer, and Charles Fitzgibbons, Age 8

"I was inspired by this Landsat image which demonstrates how we can use satellite imagery to remotely monitor cover crop performance, a sustainable farming practice that promotes soil health. Since I began working with NASA Harvest, NASA's Food Security and Agriculture Program, I've come to understand the critical importance of conservation agriculture and resilient farmlands in support of a food secure future for all, especially in the face of a changing climate." – Mary Mitkish, NASA Harvest Communications Lead

“I chose particular ingredients that represent the Landsat qualities that we celebrate:

The base spirit is gin because Landsat data is clean and precise. Vermouth represents our foreign collaborators. Using both lemon and lime juices signifies the diverse uses of the data. The ginger is for the land we study. The apple, well, because it’s American. The club soda makes it a long drink, for the long data record.” – Matthew Radcliff, NASA Landsat Producer

“Last year for the 50th Earth Day, I created this poster, inspired by our views of river deltas -- many captured by Landsat satellites -- which are particularly beautiful and evocative of water coursing through our land like a circulation system of nature. In 2000, Landsat 7 took one of my favorite images of the Lena Delta, which is the basis for this art.” – Jenny Mottar, Art Director for NASA Science

Are you feeling inspired to create yet? We’re so excited to see your #LandsatCraft projects! Follow NASA Earth on Twitter, Facebook, and Instagram to see if your art is shared!

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10 Things Einstein Got Right

One hundred years ago, on May 29, 1919, astronomers observed a total solar eclipse in an ambitious  effort to test Albert Einstein’s general theory of relativity by seeing it in action. Essentially, Einstein thought space and time were intertwined in an infinite “fabric,” like an outstretched blanket. A massive object such as the Sun bends the spacetime blanket with its gravity, such that light no longer travels in a straight line as it passes by the Sun.

This means the apparent positions of background stars seen close to the Sun in the sky – including during a solar eclipse – should seem slightly shifted in the absence of the Sun, because the Sun’s gravity bends light. But until the eclipse experiment, no one was able to test Einstein’s theory of general relativity, as no one could see stars near the Sun in the daytime otherwise.

The world celebrated the results of this eclipse experiment— a victory for Einstein, and the dawning of a new era of our understanding of the universe.

General relativity has many important consequences for what we see in the cosmos and how we make discoveries in deep space today. The same is true for Einstein's slightly older theory, special relativity, with its widely celebrated equation E=mc². Here are 10 things that result from Einstein’s theories of relativity:

1. Universal Speed Limit

Einstein's famous equation E=mc² contains "c," the speed of light in a vacuum. Although light comes in many flavors – from the rainbow of colors humans can see to the radio waves that transmit spacecraft data – Einstein said all light must obey the speed limit of 186,000 miles (300,000 kilometers) per second. So, even if two particles of light carry very different amounts of energy, they will travel at the same speed.

This has been shown experimentally in space. In 2009, our Fermi Gamma-ray Space Telescope detected two photons at virtually the same moment, with one carrying a million times more energy than the other. They both came from a high-energy region near the collision of two neutron stars about 7 billion years ago. A neutron star is the highly dense remnant of a star that has exploded. While other theories posited that space-time itself has a "foamy" texture that might slow down more energetic particles, Fermi's observations found in favor of Einstein.

2. Strong Lensing

Just like the Sun bends the light from distant stars that pass close to it, a massive object like a galaxy distorts the light from another object that is much farther away. In some cases, this phenomenon can actually help us unveil new galaxies. We say that the closer object acts like a “lens,” acting like a telescope that reveals the more distant object. Entire clusters of galaxies can be lensed and act as lenses, too.

When the lensing object appears close enough to the more distant object in the sky, we actually see multiple images of that faraway object. In 1979, scientists first observed a double image of a quasar, a very bright object at the center of a galaxy that involves a supermassive black hole feeding off a disk of inflowing gas. These apparent copies of the distant object change in brightness if the original object is changing, but not all at once, because of how space itself is bent by the foreground object’s gravity.

Sometimes, when a distant celestial object is precisely aligned with another object, we see light bent into an “Einstein ring” or arc. In this image from our Hubble Space Telescope, the sweeping arc of light represents a distant galaxy that has been lensed, forming a “smiley face” with other galaxies.

3. Weak Lensing

When a massive object acts as a lens for a farther object, but the objects are not specially aligned with respect to our view, only one image of the distant object is projected. This happens much more often. The closer object’s gravity makes the background object look larger and more stretched than it really is. This is called “weak lensing.”

Weak lensing is very important for studying some of the biggest mysteries of the universe: dark matter and dark energy. Dark matter is an invisible material that only interacts with regular matter through gravity, and holds together entire galaxies and groups of galaxies like a cosmic glue. Dark energy behaves like the opposite of gravity, making objects recede from each other. Three upcoming observatories -- Our Wide Field Infrared Survey Telescope, WFIRST, mission, the European-led Euclid space mission with NASA participation, and the ground-based Large Synoptic Survey Telescope --- will be key players in this effort. By surveying distortions of weakly lensed galaxies across the universe, scientists can characterize the effects of these persistently puzzling phenomena.

Gravitational lensing in general will also enable NASA’s James Webb Space telescope to look for some of the very first stars and galaxies of the universe.

4. Microlensing

So far, we’ve been talking about giant objects acting like magnifying lenses for other giant objects. But stars can also “lens” other stars, including stars that have planets around them. When light from a background star gets “lensed” by a closer star in the foreground, there is an increase in the background star’s brightness. If that foreground star also has a planet orbiting it, then telescopes can detect an extra bump in the background star’s light, caused by the orbiting planet. This technique for finding exoplanets, which are planets around stars other than our own, is called “microlensing.”

Our Spitzer Space Telescope, in collaboration with ground-based observatories, found an “iceball” planet through microlensing. While microlensing has so far found less than 100 confirmed planets,  WFIRST could find more than 1,000 new exoplanets using this technique.

5. Black Holes

The very existence of black holes, extremely dense objects from which no light can escape, is a prediction of general relativity. They represent the most extreme distortions of the fabric of space-time, and are especially famous for how their immense gravity affects light in weird ways that only Einstein’s theory could explain.

In 2019 the Event Horizon Telescope international collaboration, supported by the National Science Foundation and other partners, unveiled the first image of a black hole’s event horizon, the border that defines a black hole’s “point of no return” for nearby material. NASA's Chandra X-ray Observatory, Nuclear Spectroscopic Telescope Array (NuSTAR), Neil Gehrels Swift Observatory, and Fermi Gamma-ray Space Telescope all looked at the same black hole in a coordinated effort, and researchers are still analyzing the results.

6. Relativistic Jets

This Spitzer image shows the galaxy Messier 87 (M87) in infrared light, which has a supermassive black hole at its center. Around the black hole is a disk of extremely hot gas, as well as two jets of material shooting out in opposite directions. One of the jets, visible on the right of the image, is pointing almost exactly toward Earth. Its enhanced brightness is due to the emission of light from particles traveling toward the observer at near the speed of light, an effect called “relativistic beaming.” By contrast, the other jet is invisible at all wavelengths because it is traveling away from the observer near the speed of light. The details of how such jets work are still mysterious, and scientists will continue studying black holes for more clues. 

7. A Gravitational Vortex

Speaking of black holes, their gravity is so intense that they make infalling material “wobble” around them. Like a spoon stirring honey, where honey is the space around a black hole, the black hole’s distortion of space has a wobbling effect on material orbiting the black hole. Until recently, this was only theoretical. But in 2016, an international team of scientists using European Space Agency's XMM-Newton and our Nuclear Spectroscopic Telescope Array (NUSTAR) announced they had observed the signature of wobbling matter for the first time. Scientists will continue studying these odd effects of black holes to further probe Einstein’s ideas firsthand.

Incidentally, this wobbling of material around a black hole is similar to how Einstein explained Mercury’s odd orbit. As the closest planet to the Sun, Mercury feels the most gravitational tug from the Sun, and so its orbit’s orientation is slowly rotating around the Sun, creating a wobble.

 8. Gravitational Waves

Ripples through space-time called gravitational waves were hypothesized by Einstein about 100 years ago, but not actually observed until recently. In 2016, an international collaboration of astronomers working with the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors announced a landmark discovery: This enormous experiment detected the subtle signal of gravitational waves that had been traveling for 1.3 billion years after two black holes merged in a cataclysmic event. This opened a brand new door in an area of science called multi-messenger astronomy, in which both gravitational waves and light can be studied.

For example, our telescopes collaborated to measure light from two neutron stars merging after LIGO detected gravitational wave signals from the event, as announced in 2017. Given that gravitational waves from this event were detected mere 1.7 seconds before gamma rays from the merger, after both traveled 140 million light-years, scientists concluded Einstein was right about something else: gravitational waves and light waves travel at the same speed.

9. The Sun Delaying Radio Signals

Planetary exploration spacecraft have also shown Einstein to be right about general relativity. Because spacecraft communicate with Earth using light, in the form of radio waves, they present great opportunities to see whether the gravity of a massive object like the Sun changes light’s path.  

In 1970, our Jet Propulsion Laboratory announced that Mariner VI and VII, which completed flybys of Mars in 1969, had conducted experiments using radio signals — and also agreed with Einstein. Using NASA’s Deep Space Network (DSN), the two Mariners took several hundred radio measurements for this purpose. Researchers measured the time it took for radio signals to travel from the DSN dish in Goldstone, California, to the spacecraft and back. As Einstein would have predicted, there was a delay in the total roundtrip time because of the Sun’s gravity. For Mariner VI, the maximum delay was 204 microseconds, which, while far less than a single second, aligned almost exactly with what Einstein’s theory would anticipate.

In 1979, the Viking landers performed an even more accurate experiment along these lines. Then, in 2003 a group of scientists used NASA’s Cassini Spacecraft to repeat these kinds of radio science experiments with 50 times greater precision than Viking. It’s clear that Einstein’s theory has held up! 

10. Proof from Orbiting Earth

In 2004, we launched a spacecraft called Gravity Probe B specifically designed to watch Einstein’s theory play out in the orbit of Earth. The theory goes that Earth, a rotating body, should be pulling the fabric of space-time around it as it spins, in addition to distorting light with its gravity.

The spacecraft had four gyroscopes and pointed at the star IM Pegasi while orbiting Earth over the poles. In this experiment, if Einstein had been wrong, these gyroscopes would have always pointed in the same direction. But in 2011, scientists announced they had observed tiny changes in the gyroscopes’ directions as a consequence of Earth, because of its gravity, dragging space-time around it.

BONUS: Your GPS! Speaking of time delays, the GPS (global positioning system) on your phone or in your car relies on Einstein’s theories for accuracy. In order to know where you are, you need a receiver – like your phone, a ground station and a network of satellites orbiting Earth to send and receive signals. But according to general relativity, because of Earth’s gravity curving spacetime, satellites experience time moving slightly faster than on Earth. At the same time, special relativity would say time moves slower for objects that move much faster than others.

When scientists worked out the net effect of these forces, they found that the satellites’ clocks would always be a tiny bit ahead of clocks on Earth. While the difference per day is a matter of millionths of a second, that change really adds up. If GPS didn’t have relativity built into its technology, your phone would guide you miles out of your way!

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