Astronomy News

11 min read

What is Dark Energy? Inside our accelerating, expanding Universe

Some 13.8 billion years ago, the universe began with a rapid expansion we call the big bang. After this initial expansion, which lasted a fraction of a second, gravity started to slow the universe down. But the cosmos wouldn’t stay this way. Nine billion years after the universe began, its expansion started to speed up, driven by an unknown force that scientists have named dark energy.

But what exactly is dark energy?

The short answer is: We don’t know. But we do know that it exists, it’s making the universe expand at an accelerating rate, and approximately 68.3 to 70% of the universe is dark energy.

The history of the universe is outlined in this infographic. NASA A Brief History It All Started With Cepheids

Dark energy wasn’t discovered until the late 1990s. But its origin in scientific study stretches all the way back to 1912 when American astronomer Henrietta Swan Leavitt made an important discovery using Cepheid variables, a class of stars whose brightness fluctuates with a regularity that depends on the star’s brightness.

All Cepheid stars with a certain period (a Cepheid’s period is the time it takes to go from bright, to dim, and bright again) have the same absolute magnitude, or luminosity – the amount of light they put out. Leavitt measured these stars and proved that there is a relationship between their regular period of brightness and luminosity. Leavitt’s findings made it possible for astronomers to use a star’s period and luminosity to measure the distances between us and Cepheid stars in far-off galaxies (and our own Milky Way).

Around this same time in history, astronomer Vesto Slipher observed spiral galaxies using his telescope’s spectrograph, a device that splits light into the colors that make it up, much like the way a prism splits light into a rainbow. He used the spectrograph, a relatively recent invention at the time, to see the different wavelengths of light coming from the galaxies in different spectral lines. With his observations, Silpher was the first astronomer to observe how quickly the galaxy was moving away from us, called redshift, in distant galaxies. These observations would prove to be critical for many future scientific breakthroughs, including the discovery of dark energy.

Redshift is a term used when astronomical objects are moving away from us and the light coming from those objects stretches out. Light behaves like a wave, and red light has the longest wavelength. So, the light coming from objects moving away from us has a longer wavelength, stretching to the “red end” of the electromagnetic.

Discovering an Expanding Universe

The discovery of galactic redshift, the period-luminosity relation of Cepheid variables, and a newfound ability to gauge a star or galaxy’s distance eventually played a role in astronomers observing that galaxies were getting farther away from us over time, which showed how the universe was expanding. In the years that followed, different scientists around the world started to put the pieces of an expanding universe together.

In 1922, Russian scientist and mathematician Alexander Friedmann published a paper detailing multiple possibilities for the history of the universe. The paper, which was based on Albert Einstein’s theory of general relativity published in 1917, included the possibility that the universe is expanding.

In 1927, Belgian astronomer Georges Lemaître, who is said to have been unaware of Friedmann’s work, published a paper also factoring in Einstein’s theory of general relativity. And, while Einstein stated in his theory that the universe was static, Lemaître showed how the equations in Einstein’s theory actually support the idea that the universe is not static but, in fact, is actually expanding.

Astronomer Edwin Hubble confirmed that the universe was expanding in 1929 using observations made by his associate, astronomer Milton Humason. Humason measured the redshift of spiral galaxies. Hubble and Humason then studied Cepheid stars in those galaxies, using the stars to determine the distance of their galaxies (or nebulae, as they called them). They compared the distances of these galaxies to their redshift and tracked how the farther away an object is, the bigger its redshift and the faster it is moving away from us. The pair found that objects like galaxies are moving away from Earth faster the farther away they are, at upwards of hundreds of thousands of miles per second – an observation now known as Hubble’s Law, or the Hubble- Lemaître law. The universe, they confirmed, is really expanding.

This composite image features one of the most complicated and dramatic collisions between galaxy clusters ever seen. Known officially as Abell 2744, this system has been dubbed Pandora’s Cluster because of the wide variety of different structures found. Data from Chandra (red) show gas with temperatures of millions of degrees. In blue is a map showing the total mass concentration (mostly dark matter) based on data from the Hubble Space Telescope, the Very Large Telescope (VLT), and the Subaru telescope. Optical data from HST and VLT also show the constituent galaxies of the clusters. Astronomers think at least four galaxy clusters coming from a variety of directions are involved with this collision. Expansion is Speeding Up, Supernovae Show

Scientists previously thought that the universe’s expansion would likely be slowed down by gravity over time, an expectation backed by Einstein’s theory of general relativity. But in 1998, everything changed when two different teams of astronomers observing far-off supernovae noticed that (at a certain redshift) the stellar explosions were dimmer than expected. These groups were led by astronomers Adam Riess, Saul Perlmutter, and Brian Schmidt. This trio won the 2011 Nobel Prize in Physics for this work.

While dim supernovae might not seem like a major find, these astronomers were looking at Type 1a supernovae, which are known to have a certain level of luminosity. So they knew that there must be another factor making these objects appear dimmer. Scientists can determine distance (and speed) using an objects’ brightness, and dimmer objects are typically farther away (though surrounding dust and other factors can cause an object to dim).

This led the scientists to conclude that these supernovae were just much farther away than they expected by looking at their redshifts.

Using the objects’ brightness, the researchers determined the distance of these supernovae. And using the spectrum, they were able to figure out the objects’ redshift and, therefore, how fast they were moving away from us. They found that the supernovae were not as close as expected, meaning they had traveled farther away from us faster than ancitipated. These observations led scientists to ultimately conclude that the universe itself must be expanding faster over time.

While other possible explanations for these observations have been explored, astronomers studying even more distant supernovae or other cosmic phenomena in more recent years continued to gather evidence and build support for the idea that the universe is expanding faster over time, a phenomenon now called cosmic acceleration. 

But, as scientists built up a case for cosmic acceleration, they also asked: Why? What could be driving the universe to stretch out faster over time?

Enter dark energy.

What Exactly is Dark Energy?

Right now, dark energy is just the name that astronomers gave to the mysterious “something” that is causing the universe to expand at an accelerated rate.

Dark energy has been described by some as having the effect of a negative pressure that is pushing space outward. However, we don’t know if dark energy has the effect of any type of force at all. There are many ideas floating around about what dark energy could possibly be. Here are four leading explanations for dark energy. Keep in mind that it’s possible it’s something else entirely.

Vacuum Energy:

Some scientists think that dark energy is a fundamental, ever-present background energy in space known as vacuum energy, which could be equal to the cosmological constant, a mathematical term in the equations of Einstein’s theory of general relativity. Originally, the constant existed to counterbalance gravity, resulting in a static universe. But when Hubble confirmed that the universe was actually expanding, Einstein removed the constant, calling it “my biggest blunder,” according to physicist George Gamow.

But when it was later discovered that the universe’s expansion was actually accelerating, some scientists suggested that there might actually be a non-zero value to the previously-discredited cosmological constant. They suggested that this additional force would be necessary to accelerate the expansion of the universe. This theorized that this mystery component could be attributed to something called “vacuum energy,” which is a theoretical background energy permeating all of space.

Space is never exactly empty. According to quantum field theory, there are virtual particles, or pairs of particles and antiparticles. It’s thought that these virtual particles cancel each other out almost as soon as they crop up in the universe, and that this act of popping in and out of existence could be made possible by “vacuum energy” that fills the cosmos and pushes space outward.

While this theory has been a popular topic of discussion, scientists investigating this option have calculated how much vacuum energy there should theoretically be in space. They showed that there should either be so much vacuum energy that, at the very beginning, the universe would have expanded outwards so quickly and with so much force that no stars or galaxies could have formed, or… there should be absolutely none. This means that the amount of vacuum energy in the cosmos must be much smaller than it is in these predictions. However, this discrepancy has yet to be solved and has even earned the moniker “the cosmological constant problem.”

Quintessence:

Some scientists think that dark energy could be a type of energy fluid or field that fills space, behaves in an opposite way to normal matter, and can vary in its amount and distribution throughout both time and space. This hypothesized version of dark energy has been nicknamed quintessence after the theoretical fifth element discussed by ancient Greek philosophers.

It’s even been suggested by some scientists that quintessence could be some combination of dark energy and dark matter, though the two are currently considered completely separate from one another. While the two are both major mysteries to scientists, dark matter is thought to make up about 85% of all matter in the universe.

Space Wrinkles:

Some scientists think that dark energy could be a sort of defect in the fabric of the universe itself; defects like cosmic strings, which are hypothetical one-dimensional “wrinkles” thought to have formed in the early universe. 

A Flaw in General Relativity:

Some scientists think that dark energy isn’t something physical that we can discover. Rather, they think there could be an issue with general relativity and Einstein’s theory of gravity and how it works on the scale of the observable universe. Within this explanation, scientists think that it’s possible to modify our understanding of gravity in a way that explains observations of the universe made without the need for dark energy. Einstein actually proposed such an idea in 1919 called unimodular gravity, a modified version of general relativity that scientists today think wouldn’t require dark energy to make sense of the universe.

The Future

Dark energy is one of the great mysteries of the universe. For decades, scientists have theorized about our expanding universe. Now, for the first time ever, we have tools powerful enough to put these theories to the test and really investigate the big question: “what is dark energy?”

NASA plays a critical role in the ESA (European Space Agency) mission Euclid (launched in 2023), which will make a 3D map of the universe to see how matter has been pulled apart by dark energy over time. This map will include observations of billions of galaxies found up to 10 billion light-years from Earth.

NASA’s Nancy Grace Roman Space Telescope, set to launch by May 2027, is designed to investigate dark energy, among many other science topics, and will also create a 3D dark matter map. Roman’s resolution will be as sharp as NASA’s Hubble Space Telescope’s, but with a field of view 100 times larger, allowing it to capture more expansive images of the universe. This will allow scientists to map how matter is structured and spread across the universe and explore how dark energy behaves and has changed over time. Roman will also conduct an additional survey to detect Type Ia supernovae

In addition to NASA’s missions and efforts, the Vera C. Rubin Observatory, supported by a large collaboration that includes the U.S. National Science Foundation, which is currently under construction in Chile, is also poised to support our growing understanding of dark energy. The ground-based observatory is expected to be operational in 2025.

The combined efforts of Euclid, Roman, and Rubin will usher in a new “golden age” of cosmology, in which scientists will collect more detailed information than ever about the great mysteries of dark energy.

Additionally, NASA’s James Webb Space Telescope (launched in 2021), the world’s most powerful and largest space telescope, aims to make contributions to several areas of research, and will contribute to studies of dark energy.

NASA’s SPHEREx (the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) mission, scheduled to launch no later than April 2025, aims to investigate the origins of the universe. Scientists expect that the data collected with SPHEREx, which will survey the entire sky in near-infrared light, including over 450 million galaxies, could help to further our understanding of dark energy.

NASA also supports a citizen science project called Dark Energy Explorers, which enables anyone in the world, even those who have no scientific training, to help in the search for dark energy answers.

*A brief note*

Lastly, to clarify, dark energy is not the same as dark matter. Their main similarity is that we don’t yet know what they are!

By Chelsea Gohd
NASA’s Jet Propulsion Laboratory

Share

• 
  
  
• 
  
  
• 
  
  
• 
  
  

Details Last Updated Feb 05, 2024 Related Terms

• Dark Energy
• Dark Matter
• Euclid
• Galaxies
• James Webb Space Telescope (JWST)
• Nancy Grace Roman Space Telescope
• SPHEREx (Spectro-Photometer for the History of the Universe and Ices Explorer)
• Stellar Evolution
• The Big Bang
• The Universe

Explore More 2 min read Hubble Views a Dim but Distinct Galaxy

Article


3 days ago

2 min read Hubble Sees a Merged Galaxy

Article


4 days ago

2 min read Hubble Captures a Suspected Galaxy Encounter

Article


5 days ago

Keep Exploring Discover More Topics From NASA

Missions

Humans in Space

Climate Change

Solar System

Nature, Published online: 05 February 2024; doi:10.1038/d41586-024-00315-1

Reviewers will likely approve only one in every nine research proposals submitted in latest application cycle.

Scientists have analysed the stars that an upcoming NASA telescope will target in its search for biosignatures, narrowing down the candidates for those that could host potential extraterrestrial life

The Lisa project to detect gravitational waves will be one of the most complex ever space missions.

Astronomers have, for the first time, made a direct measurement of the mass of a distant black hole, one so far away that light from its surroundings took 11 billion years to reach us. The team, led by Taro Shimizu at the Max Planck Institute for Extraterrestrial Physics in Germany, found the black hole, called J0920, to have a mass of about 320 million times that of the Sun. This achievement, described in a paper published today in Nature, has been made possible thanks to GRAVITY+, a series of ongoing upgrades to ESO’s Very Large Telescope Interferometer (VLTI) and its GRAVITY instrument.

To directly measure the mass of a black hole, astronomers use telescopes to track the movement of gas and stars around it. The faster these move, the more mass is encased within the material’s orbit. This technique has been used to measure the mass of nearby black holes, including the one at the centre of the Milky Way. At very remote distances, however, this motion is extremely hard to observe. This means similar direct measurements of the mass of distant black holes, which provide a window into a period in the history of the Universe when galaxies and black holes were rapidly growing, have not been possible until now.

The direct measurement of J0920’s mass was only possible with the first set of GRAVITY+ improvements. These upgrades have allowed astronomers to observe the faint, distant gas around the black hole with greater accuracy than ever before by using a technique called wide-field, off-axis fringe tracking. Measuring the mass of J0920 accurately is a first step to help astronomers understand how black holes and galaxies grew together at a time when the Universe was only a couple of billion years old and galaxies were still forming. For J0920, the new mass measurement reveals the black hole is about four times less massive than expected given the mass of its host galaxy; this indicates a delay in the growth of the black hole compared to the surrounding galaxy.

GRAVITY+ uses interferometry to combine the light arriving at the four 8-metre Unit Telescopes (UTs) that are part of VLTI. Once completed, it will include upgraded adaptive optics technology that will enable better correction of the blur caused by the Earth’s atmosphere and improve the contrast of observations. GRAVITY+ will also implement one new laser guide star on each of UT1-3, and will make use of one of the lasers currently installed on UT4, to observe fainter and more distant objects than currently possible.

The upgrades to GRAVITY+ are being implemented incrementally, to ensure that there are limited disruptions to the scientific operations of the VLTI. This also allows for astronomers to continually test the performance of GRAVITY+ as it comes online. The full set of upgrades is anticipated to be completed in 2025. The new features will benefit all present and future VLTI instruments and the scientists who use them.

More Information

This research was presented in a paper to appear in Nature titled “A dynamical measurement of the supermassive black hole mass in a quasar 11 billion years ago”.

The team is composed of R. Abuter (European Southern Observatory, Garching, Germany [ESO]), F. Allouche (Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France [Lagrange]), A. Amorim (Universidade de Lisboa - Faculdade de Ciências, Portugal and Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, Portugal [CENTRA]), C. Bailet (Lagrange), A. Berdeu (Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, France [LESIA]), J. P. Berger (Univ. Grenoble Alpes, CNRS, France [UGA]), P. Berio (Lagrange), A. Bigioli (Institute of Astronomy, KU Leuven, Belgium [KU Leuven]), O. Boebion (Lagrange), M.-L. Bolzer (Max Planck Institute for Extraterrestrial Physics, Germany [MPE], Department of Physics, Technical University Munich, Germany [TUM] and Univ. Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, France [CRAL]), H. Bonnet (ESO), G. Bourdarot (MPE), P. Bourget (European Southern Observatory, Chile [ESO Chile]), W. Brandner (Max Planck Institute for Astronomy, Germany [MPIA]), Y. Cao (MPE), R. Conzelman (ESO), M. Comin (ESO), Y. Clénet (LESIA), B. Courtney-Barrer (ESO Chile and Research School of Astronomy and Astrophysics, College of Science, Australian National University, Australia [ANU]), R. Davies (MPE), D. Defrère (KU Leuven), A. Delboulbé (UGA), F. Delplancke-Ströbele (ESO), R. Dembet (LESIA), J. Dexter (Department of Astrophysical & Planetary Sciences, JILA, University of Colorado, USA), P. T. de Zeeuw (Leiden University, The Netherlands), A. Drescher (MPE), A. Eckart (Max Planck Institute for Radio Astronomy, Germany [MPIfR] and 1st Institute of Physics, University of Cologne, Germany [Cologne]), C. Édouard (LESIA), F. Eisenhauer (MPE), M. Fabricius (MPE), H. Feuchtgruber (MPE), G. Finger (MPE), N. M. Förster Schreiber (MPE), P. Garcia (Faculdade de Engenharia, Universidade do Porto, Portugal [FEUP] and CENTRA), R. Garcia Lopez (School of Physics, University College Dublin, Ireland), F. Gao (MPIfR), E. Gendron (LESIA), R. Genzel (MPE and Departments of Physics and Astronomy, University of California, USA), J.P. Gil (ESO Chile), S. Gillessen (MPE), T. Gomes (CENTRA and FEUP), F. Gonté (ESO), C. Gouvret (Lagrange), P. Guajardo (ESO Chile), S. Guieu (IPAG), W. Hackenberg (ESO), N. Haddad (ESO Chile), M. Hartl (MPE), X. Haubois (ESO Chile), F. Haußmann (MPE), G. Heißel (LESIA and Advanced Concepts Team, European Space Agency, TEC-SF, ESTEC, The Netherlands), T. Henning (MPIA), S. Hippler (MPIA), S.F. Hönig (School of Physics & Astronomy, University of Southampton, UK [Southampton]), M. Horrobin (Cologne), N. Hubin (ESO), E. Jacqmart (Lagrange), L. Jocou (IPAG), A. Kaufer (ESO Chile), P. Kervella (LESIA), J. Kolb (ESO), H. Korhonen (ESO Chile), S. Lacour (ESO and LESIA), S. Lagarde (Lagrange), O. Lai (Lagrange), V. Lapeyrère (LESIA), R. Laugier (KU Leuven), J.-B. Le Bouquin (IPAG), J. Leftley (Lagrange), P. Léna (LESIA), S. Lewis (ESO), D. Liu (MPE), B. Lopez (Lagrange), D. Lutz (MPE), Y. Magnard (IPAG), F. Mang (MPE and TUM), A. Marcotto (Lagrange), D. Maurel (IPAG), A. Mérand (ESO), F. Millour (Lagrange), N. More (MPE), H. Netzer (School of Physics and Astronomy, Tel Aviv University, Israel [TAU]), H. Nowacki (IPAG), M. Nowak (Institute of Astronomy, University of Cambridge, UK), S. Oberti (ESO), T. Ott (MPE), L. Pallanca (ESO Chile), T. Paumard (LESIA), K. Perraut (IPAG), G. Perrin (LESIA), R. Petrov (Lagrange), O. Pfuhl (ESO), N. Pourré (IPAG), S. Rabien (MPE), C. Rau (MPE), M. Riquelme (ESO), S. Robbe-Dubois (Lagrange), S. Rochat (IPAG), M. Salman (KU Leuven), J. Sanchez-Bermudez (Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico and MPIA), D.J.D. Santos (MPE), S. Scheithauer (MPIA), M. Schöller (ESO), J. Schubert (MPE), N. Schuhler (ESO Chile), J. Shangguan (MPE), P. Shchekaturov (ESO), T.T. Shimizu (MPE), A. Sevin (LESIA), F. Soulez (CRAL), A. Spang (Lagrange), E. Stadler (IPAG), A. Sternberg (TAU and Center for Computational Astrophysics, Flatiron Institute, USA), C. Straubmeier (Cologne), E. Sturm (MPE), C. Sykes (Southampton), L.J. Tacconi (MPE), K.R.W. Tristram (ESO Chile), F. Vincent (LESIA), S. von Fellenberg (MPIfR), S. Uysal (MPE), F. Widmann (MPE), E. Wieprecht (MPE), E. Wiezorrek (MPE), J. Woillez (ESO), and G. Zins (ESO).

The GRAVITY+ upgrades are designed and built by the following institutes together with ESO:

• Max Planck Institute for Extraterrestrial Physics; Max Planck Institute for Astronomy; the University of Cologne (Germany)
• Institut National des Sciences de l'Univers, French National Center for Scientific Research; Institut de Planétologie et d'Astrophysique de Grenoble; Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique; the Lagrange Laboratory; the Centre de Recherche Astrophysique de Lyon (France)
• Instituto Superior Técnico’s Centre for Astrophysics and Gravitation; University of Lisbon; University of Porto (Portugal)
• University of Southampton (UK)
• Katholieke Universiteit Leuven (Belgium)

Nature, Published online: 29 January 2024; doi:10.1038/s41586-024-07053-4

A dynamical measure of the black hole mass in a quasar 11 billion years ago

SLIM was put into hibernation after landing on the moon upside down, but it woke up when sunlight hit its solar panels

Astronomers have used the James Webb Space Telescope to take astonishingly detailed images of spiral galaxies, revealing how and where they spark star formation

After nearly three years of exploring Mars, NASA’s Ingenuity helicopter has taken its final flight – but its astounding performance is a good sign for future drones on other worlds

Light from hydrogen in the early universe has baffled astronomers, but researchers have spotted interacting galaxies that could explain how it makes its way to us

The lander has begun sending photos, including that of a nearby rock nicknamed "toy poodle".

1 min read

Preparations for Next Moonwalk Simulations Underway (and Underwater)

On Jan. 19, 2024, at 10:20 a.m. EST, the JAXA (Japan Aerospace Exploration Agency) Smart Lander for Investigating Moon (SLIM) landed on the lunar surface. Five days later, NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft passed over the landing site and photographed SLIM.

NASA’s Lunar Reconnaissance Orbiter captured this image of the JAXA (Japan Aerospace Exploration Agency) SLIM lander on the Moon’s surface on Jan. 24, 2024. SLIM landed at 13.3160 degrees south latitude, 25.2510 degrees east longitude, at an elevation of minus 2,992 feet (minus 912 meters). The image is 2,887 feet wide (880 meters), and lunar north is up. (LROC NAC frame M14607392143L)NASA/Goddard/Arizona State University

LRO acquired the image at an altitude of about 50 miles (80 km). Bright streaks on the left side of the image are rocky material ejected from the nearby, relatively young Shioli crater.

Japan is the fifth nation to complete a soft landing on the lunar surface.

This image pair shows LRO views of the area surrounding the SLIM site before (frame M1254087075L) and after (frame M1460739214L) its landing. Note the slight change in reflectance around the lander due to engine exhaust sweeping the surface. These images are enlarged by a factor of two, and are about 1,444 feet (440 meters) wide.NASA/Goddard/Arizona State University A composite image dividing the before image from after. Features that are the same in both images disappear, highlighting the changes in surface brightness from the rocket plume. The image is 2,887 feet wide (880 meters), and lunar north is up.NASA/Goddard/Arizona State University

LRO is managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland, for the agency’s Science Mission Directorate at NASA Headquarters in Washington. Launched on June 18, 2009, LRO has collected a treasure trove of data with its seven powerful instruments, making an invaluable contribution to our knowledge about the Moon. Arizona State University manages and operates the Lunar Reconnaissance Orbiter Camera, LROC.

More on this story from Arizona State University's LRO Camera website

Media Contact:
Nancy N. Jones
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Facebook logo @NASAGoddard@NASAMoon @NASAGoddard@NASAMoon Instagram logo @NASAGoddard@NASASolarSystem Share

Details Last Updated Jan 26, 2024 EditorMadison ArnoldContactNancy N. Jonesnancy.n.jones@nasa.govLocationGoddard Space Flight Center Related Terms

• Lunar Reconnaissance Orbiter (LRO)
• Earth's Moon
• Goddard Space Flight Center
• The Solar System

Nature, Published online: 26 January 2024; doi:10.1038/d41586-024-00254-x

An experiment has been given the go ahead to send lasers to orbit the Sun to hunt for gigantic ripples in space-time.

The first vehicle to achieve powered flight on another planet suffers rotor damage three years into tour.

3 Min Read Landing On Mars: A Tricky Feat! Perseverance Rover’s Entry, Descent and Landing Profile: This illustration shows the events that occur in the final minutes of the nearly seven-month journey that NASA’s Perseverance rover takes to Mars.

In honor of Ingenuity’s final flight on The Red Planet, learn from Dave Prosper about what it takes to land on Mars.

The Perseverance rover and Ingenuity helicopter landed in Mars’s Jezero crater on February 18, 2021, NASA’s latest mission to explore the red planet. Landing on Mars is an incredibly difficult feat that has challenged engineers for decades: while missions like Curiosity have succeeded, its surface is littered with the wreckage of many failures as well. Why is landing on Mars so difficult?

Mars presents a unique problem to potential landers as it possesses a relatively large mass and a thin, but not insubstantial, atmosphere. The atmosphere is thick enough that spacecraft are stuffed inside a streamlined aeroshell sporting a protective heat shield to prevent burning up upon entry – but that same atmosphere is not thick enough to rely on parachutes alone for a safe landing, since they can’t catch sufficient air to slow down quickly enough. This is even worse for larger explorers like Perseverance, weighing in at 2,260 lbs (1,025 kg). Fortunately, engineers have crafted some ingenious landing methods over the decades to allow their spacecraft to survive what is called Entry, Descent, and Landing (EDL).

Illustrations of the Entry, Descent, and Landing (EDL) sequences for Viking in 1976, NASA

The Viking landers touched down on Mars in 1976 using heat shields, parachutes, and retrorockets. Despite using large parachutes, the large Viking landers fired retrorockets at the end to land at a safe speed. This complex combination has been followed by almost every mission since, but subsequent missions have innovated in the landing segment. The 1997 Mars Pathfinder mission added airbags in conjunction with parachutes and retrorockets to safely bounce its way to a landing on the Martian surface. Then three sturdy “petals” ensured the lander was pushed into an upright position after landing on an ancient floodplain. The Opportunity and Spirit missions used a very similar method to place their rovers on the Martian surface in 2004. Phoenix (2008) and Insight (2018) actually utilized Viking-style landings.

Perseverance Rover’s Entry, Descent and Landing Profile: This illustration shows the events that occur in the final minutes of the nearly seven-month journey that NASA’s Perseverance rover takes to Mars. NASA/JPL-Caltech

The large and heavy Curiosity rover required extra power at the end to safely land the car-sized rover, and so the daring “Sky Crane” deployment system was successfully used in 2012. After an initial descent using a massive heat shield and parachute, powerful retrorockets finished slowing down the spacecraft to about two miles per hour. The Sky Crane then safely lowered the rover down to the Martian surface using a strong cable. Its job done, the Sky Crane then flew off and crash-landed a safe distance away. Having proved the efficacy of the Sky Crane system, NASA used this same method to attempt a safe landing for Perseverance in February 2021!

To rediscover the Mars 2020 mission, visit: https://mars.nasa.gov/mars2020/

Originally posted by Dave Prosper: December 2021

Last Updated by Kat Troche: January 2024

Nature, Published online: 25 January 2024; doi:10.1038/d41586-024-00223-4

Data from an African observatory show that jets from a collapsed star are capable of producing some of the Galaxy’s fastest particles.

Nature, Published online: 26 January 2024; doi:10.1038/d41586-024-00248-9

The record-setting Mars helicopter Ingenuity broke during a final, fatal flight.

We keep finding pancake-like objects in the solar system and it could be because they form in a certain way – from spinning clouds of pebbles

Observations of the microquasar SS 433 provide clues to how these small black holes accelerate electrons to produce high-energy jets

Japan’s Smart Lander for Investigating Moon (SLIM) didn’t last long after it landed on the surface of the moon, but it released two rovers – one that hops and one that rolls – that took images on the lunar surface