Lunar Eclipses: What Are They; When is the Next One?

Skywatcher and photographer David Paleino snapped this view of the total lunar eclipse of June 15, 2011 from Italy using a Fujifilm FinePix S2000HD camera. Credit: David Paleino View full size image

Lunar eclipses occur when Earth's shadow blocks the sun’s light, which otherwise reflects off the moon. There are three types — total, partial and penumbral — with the most dramatic being a total lunar eclipse, in which Earth’s shadow completely covers the moon.

The last lunar eclipse was on Oct. 8, 2014. [Related: Blood Moon Photos: Total Lunar Eclipse Thrills Skywatchers]

The next lunar eclipse is on April 4, 2015. It will be a total eclipse, best seen from the Pacific Ocean and bordering regions in the Americas, Asia and Australia.

Throughout history, eclipses have inspired awe and even fear, especially when total lunar eclipses turned the moon blood-red, an effect that terrified people who had no understanding of what causes an eclipse and therefore blamed the events on this god or that. Below, you’ll find the science and history of lunar eclipses, learn how they work, and see a list of the next ones on tap. [See also our guide to Solar Eclipses.]

This montage of images taken by skywatcher Kieth Burns shows the Dec. 20, 2010 total lunar eclipse. The photos won a NASA contest to become an official NASA/JPL wallpaper for the public.
Credit: NASA/JPL-via Kieth Burns

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What is a lunar eclipse?

A lunar eclipse can occur only at full moon. A total lunar eclipse can happen only when the sun, Earth and moon are perfectly lined up — anything less than perfection creates a partial lunar eclipse or no eclipse at all. Some understanding of simple celestial mechanics explains how lunar eclipses work. [Infographic: Total Eclipse of the Moon]

Because the moon’s orbit around Earth lies in a slightly different plane than Earth’s orbit around the sun, perfect alignment for an eclipse doesn’t occur at every full moon. A total lunar eclipse develops over time, typically a couple hours for the whole event. Here’s how it works: Earth casts two shadows that fall on the moon during a lunar eclipse: The umbra is a full, dark shadow. The penumbra is a partial outer shadow. The moon passes through these shadows in stages. The initial and final stages — when the moon is in the penumbral shadow — are not so noticeable, so the best part of an eclipse is during the middle of the event, when the moon is in the umbral shadow.

Total eclipses are a freak of cosmic happenstance. Ever since the moon formed, about 4.5 billion years ago, it has been inching away from our planet (by about 1.6 inches, or 4 centimeters per year). The setup right now is perfect: the moon is at the perfect distance for Earth’s shadow to cover the moon totally, but just barely. Billions of years from now, that won’t be the case.

Types of lunar eclipses

Total lunar eclipse: Earth’s full (umbral) shadow falls on the moon. The moon won’t completely disappear, but it will be cast in an eerie darkness that makes it easy to miss if you were not looking for the eclipse. Some sunlight passing through Earth’s atmosphere is scattered and refracted, or bent, and refocused on the moon, giving it a dim glow even during totality. If you were standing on the moon, looking back at the sun, you’d see the black disk of Earth blocking the entire sun, but you’d also see a ring of reflected light glowing around the edges of Earth — that’s the light that falls on the moon during a total lunar eclipse.

Partial lunar eclipse: Some eclipses are only partial. But even a total lunar eclipse goes through a partial phase on either side of totality. During the partial phase, the sun, Earth and moon are not quite perfectly aligned, and Earth’s shadow appears to take a bite out of the moon.

Penumbral lunar eclipse: This is the least interesting type of eclipse, because the moon is in Earth’s faint outer (penumbral) shadow. Unless you’re a seasoned skywatcher, you likely won’t notice the effect.

The blood-red moon

The moon may turn red or coppery colored during the total portion of an eclipse. The red moon is possible because while the moon is in total shadow, some light from the sun passes through Earth's atmosphere and is bent toward the moon. While other colors in the spectrum are blocked and scattered by Earth’s atmosphere, red light tends to make it through easier. The effect is to cast all the planet's sunrises and sunsets on the moon.

The moon turned a blood red over the Sossusvlei Desert Lodge on NamibRand Nature Reserve in Namibia in this stunning photo taken by skywatcher George Tucker on June 15, 2011.
Credit: George Tucker

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"The exact color that the moon appears depends on the amount of dust and clouds in the atmosphere," according to NASA scientists. "If there are extra particles in the atmosphere, from say a recent volcanic eruption, the moon will appear a darker shade of red."

Christopher Columbus leveraged a blood-red eclipse in 1504 to frighten natives on Jamaica into feeding him and his crew. It was on Columbus’ fourth and final voyage to the New World. An epidemic of shipworms ate holes in the ships of his fleet; Columbus' was forced to abandon two ships. He then beached his last two on Jamaica on June 25, 1503. The natives welcomed the castaways and fed them. But after six months, Columbus’ crew mutinied, and robbed and murdered some of the Jamaicans, who had grown weary of feeding the crew.

Columbus had an almanac that foretold a lunar eclipse on Feb. 29, 1504. He met the local chief, and told him the Christian god was angry with his people for no longer supplying food. Columbus said to expect a sign of God’s displeasure three nights later, when He would make the full moon appear "inflamed with wrath." When the blood-red moon came to pass, the natives were terrified and “with great howling and lamentation came running from every direction to the ships laden with provisions,” according to an account from Columbus’ son.

Just before the total phase of the eclipse was about to end, Columbus said God had pardoned the natives and would bring the moon back. The crew was well fed until help arrived in November and Columbus and his men sailed back to Spain.

When is the next lunar eclipse?

Here is a schedule of upcoming lunar eclipses:

April 4, 2015: Total eclipse. Visible from the Pacific Ocean and bordering regions in the Americas, Asia and Australia.

Sept. 28, 2015: Total eclipse. Visible from eastern Pacific Ocean, Americas, Europe, Africa, western Asia.

March 23, 2016: Penumbral eclipse. Visible from Asia, Australia, Pacific Ocean, western Americas.

Sept. 16, 2016: Penumbral eclipse. Visible from Europe, Africa, Asia, Australia, western Pacific Ocean.

This photo of the total lunar eclipse of Dec. 20, 2010 by Jimmy Westlake shows the blue edge to Earth's shadow set against the reddened moon.
Credit: Jimmy Westlake

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Dwarf Planet Pluto: Facts About the Icy Former Planet

Some craters and other surface features spotted on Pluto by NASA's New Horizons probe in 2015 may end up bearing the name of "Star Trek" characters, as this screenshot from a Google+ Hangout demonstrates. Credit: SETI Institute (via Google+/YouTube) View full size image

Pluto is the only dwarf planet to once have been considered a major planet. Once thought of as the ninth planet and the one most distant from the sun, Pluto is now seen as one of the largest known members of the Kuiper Belt, a shadowy disk-like zone beyond the orbit of Neptune populated by a trillion or more comets. 

Pluto was reclassified as a dwarf planet in 2006, a change widely thought of as a demotion that has attracted controversy and debate that has continued in scientific communities for the last eight years.

American astronomer Percival Lowell first caught hints of Pluto's existence in 1905 from odd deviations he observed in the orbits of Neptune and Uranus, suggesting that another world's gravity was tugging at them from beyond. He predicted its location in 1915, but died without finding it. Its discovery came in 1930 from Clyde Tombaugh at the Lowell Observatory, based on predictions from Lowell and other astronomers.

Pluto is the only world named by an 11-year-old girl, Venetia Burney of Oxford, England, who suggested to her grandfather that it get its name from the Roman god of the underworld. Her grandfather then passed the name on to Lowell Observatory. The name also honors Percival Lowell, whose initials are the first two letters of Pluto. 

Physical characteristics

Since Pluto is so far from Earth, little is known about the planet’s size or surface conditions. Pluto has an estimated diameter less than one-fifth that of Earth or only about two-thirds as wide as Earth's moon. The planets’ surface conditions probably consist of a rocky core surrounded by a mantle of water ice, with more exotic ices such as methane and nitrogen frost coating its surface. NASA’s Hubble Space Telescope also revealed evidence that Pluto’s crust could contain complex organic molecules. Chemicals such as nitrogen and methane may lay frozen beneath the icy crust.

Pluto's orbit is highly eccentric, or far from circular, which means its distance from the sun can vary considerably and at times, Pluto’s orbit will take it within the orbit of the planet Neptune. When Pluto is closer to the sun, its surface ices thaw and temporarily form a thin atmosphere, mostly of nitrogen, with some methane. Pluto's low gravity, which is a little more than one-twentieth that of Earth's, causes this atmosphere to extend much higher in altitude than Earth's. When traveling farther away from the sun, most of Pluto's atmosphere is thought to freeze and all but disappear. Still, in the time that it does have an atmosphere, Pluto can apparently experience strong winds.

Pluto's surface is one of the coldest places in the solar system at roughly minus 375 degrees F (minus 225 degrees C). For a long time, astronomers knew little about its surface because of its distance from Earth, but more is coming, bit by bit, with the Hubble Space Telescope returning images of a planet that appears reddish, yellowish and grayish in places, with a curious bright spot near the equator that might be rich in carbon monoxide frost. When compared with past images, the Hubble pictures revealed that Pluto had apparently grown redder over time, apparently due to seasonal changes.

This is the most detailed view to date of the entire surface of the dwarf planet Pluto, as constructed from multiple NASA Hubble Space Telescope photographs taken from 2002 to 2003.
Credit: NASA, ESA, and M. Buie (Southwest Research Institute)

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Orbital characteristics

Pluto's highly elliptical orbit can take it more than 49 times as far out from the sun as Earth. It actually gets closer to the sun than Neptune for 20 years out of Pluto's 248-Earth-years-long orbit, providing astronomers a rare chance to study this small, cold, distant world. So after 20 years as the eighth planet (in order going out from the sun), in 1999, Pluto crossed Neptune's orbit to become the farthest planet from the sun (until it was demoted to the status of dwarf planet).

Composition & structure

Atmospheric composition: Methane, nitrogen

Magnetic field: It remains unknown whether Pluto has a magnetic field, but its small size and slow rotation suggest it has little to none.

Chemical composition: Probably a mixture of 70 percent rock and 30 percent water ice.

Internal structure: Probably a rocky core surrounded by a mantle of water ice, with more exotic ices such as methane and nitrogen frost coating its surface.

Credit: Karl Tate, SPACE.com

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Orbit & rotation

Average distance from the sun: 3,670,050,000 miles (5,906,380,000 km) — 39.482 times that of Earth

Perihelion (closest approach to the sun): 2,756,902,000 miles (4,436,820,000 km) — 30.171 times that of Earth

Aphelion (farthest distance from the sun): 4,583,190,000 miles (7,375,930,000 km) — 48.481 times that of Earth

Pluto's moons

In 1978, astronomers discovered Pluto had a very large moon nearly half its size, dubbed Charon, named for the mythological demon who ferried souls to the underworld in Greek mythology. The huge size of Charon sometimes leads scientists to refer to Pluto and Charon as a double dwarf planet or binary system.

Pluto and Charon are just 12,200 miles (19,640 km) apart, less than the distance by flight between London and Sydney. Charon's orbit around Pluto takes 6.4 Earth days, and one Pluto rotation — a Pluto day — also takes 6.4 Earth days. This is because Charon hovers over the same spot on Pluto's surface, and the same side of Charon always faces Pluto, a phenomenon known as tidal locking.

While Pluto appears reddish, Charon seems grayish. Scientists suggest Pluto is covered with nitrogen and methane while Charon is covered with ordinary water ice. In its early days, the moon may have contained a subsurface ocean, though it probably can’t support one today.

Compared with most of solar system's planets and moons, the Pluto-Charon system is tipped on its side in relation to the sun. Also, Pluto's rotation is retrograde compared to the other worlds — it spins backward, from east to west.

In 2005, as scientists photographed Pluto with the Hubble Space Telescope in preparation for the New Horizons mission — the first spacecraft to visit Pluto and the Kuiper Belt — they discovered two other tiny moons of Pluto, now dubbed Nix and Hydra. These are two to three times farther away from Pluto than Charon, and they are thought to be just 31 to 62 miles (50 to 100 km) wide.

Scientists using Hubble discovered a fourth moon, Kerberos, in 2011. This moon is estimated to be 8 to 21 miles (13 to 34 km) in diameter. P4's orbit is between the orbits of Nix and Hydra. On July 11, 2012, a fifth moon Styx, was discovered, fueling the debate about Pluto’s status as a planet.

The four newly spotted moons may have formed from the collision that created Charon, hurled away from Pluto by the gravity of the massive moon.

Research & exploration

Pluto's distance from Earth has made it hard to see with telescopes and a daunting challenge to explore with spacecraft — NASA's New Horizonsmission will be the first probe to study Pluto, its moons, and other worlds within the Kuiper Belt. It was launched on January 2006, making its closest approach to Pluto on July 2015, and carries some of the ashes of Pluto's discoverer, Clyde Tombaugh.

The limited knowledge of Pluto creates unprecedented dangers for the exploration. Prior to the mission’s launch, scientists only knew about the existence of three moons. The discovery of Keberos and Styx during the spacecraft’s journey fueled the idea that more satellites could orbit the dwarf planet, unseen from Earth. Not only the moons, but the debris fields they may have created, could prove hazardous to New Horizons.

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'Interstellar' Sneak Peek: We Have Seen It, and It's Awesome

A theatrical poster for the space epic "Interstellar," which is directed by Christopher Nolan and stars Matthew McConaughey (shown here). The film will be released throughout the United States on Nov. 7, 2014. Credit: Paramount Pictures View full size image

LOS ANGELES — All the buzz around the upcoming space epic "Interstellar" is understandable. The film is a great ride — big, bold, loud, dramatic and visually stunning.

The crowd at the TCL Chinese Theater here in Hollywood for a sneak-peak viewing on Thursday (Oct. 23) — a collection of journalists and actors who got an invite and fans who waited in line for ages to get in — soaked up "Interstellar" throughout its nearly three-hour running time, even erupting in cheers at several key points during the film.

In short, the feeling inside the theater seemed to be that "Interstellar," which will hit theaters nationwide in the United States on Nov. 7, doesn't disappoint despite its considerable hype. ['Interstellar': A Space Epic in Pictures]

That hype stems partly from the film's star power. "Interstellar" was directed by Christopher Nolan, who has helmed a number of commercially and critically successful films, including "Memento," "Inception" and the "Batman" Dark Knight trilogy. And it features big-name actors such as Matthew McConaughey, Anne Hathaway, Jessica Chastain and Michael Caine.

The subject matter of "Interstellar" is also responsible for some of the excitement, especially among space fans. As the film's trailers have shown, a series of crises on Earth are driving humanity toward extinction. So McConaughey's character, Cooper, leads a small band of explorers in a search for an exoplanet that could serve as a new home for our species.

This intergalactic search is aided by a journey through a wormhole — a sort of tunnel through the fabric of space-time that allows relatively rapid travel between two widely separated points. "Interstellar" also features stunning depictions of spaceflight, alien worlds and what its creators say is the most accurate visualization of a black hole ever accomplished in a mainstream movie.

In fact, the film's black hole is so visually realistic that scientists could learn a thing or two from it, said renowned theoretical physicist Kip Thorne, one of the executive producers of "Interstellar."

"We're going to write several technical papers about this — one aimed at the astrophysics community and then something for the computer-graphics community — saying, Here are some things we've discovered about gravitational lensing by rapidly spinning black holes that we never knew before," Thorne said in a video produced by Wired magazine that was released last week.

Keep checking back in with Space.com for more news about "Interstellar," including a full review and an analysis of the science in the film.

Interestingly, "Interstellar" comes out on the same day (Nov. 7) as another movie of interest to space-science fans — "Theory of Everything," a biopic about famous astrophysicist Stephen Hawking.

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See Elusive Planet Mercury Before Dawn Saturday

Mercury will be best placed for Northern Hemisphere observers on Nov. 1, 2014 just before sunrise. It will be visible for a few days before then, and for a week after. Credit: Starry Night software View full size image

Although Mercury is one of the brightest objects in the sky, even the most dedicated stargazers rarely see the innermost planet because it is usually so close to the sun.

This week is one of the rare opportunities when Mercury is relatively easy to spot. It will mean getting up before the sun, but once spotted, you will be able to follow Mercury until it is drowned out by daylight.

All apparitions of Mercury are not created equal. Because of the tilt of the ecliptic — the path that the planets follow across the sky — the inner planets, Mercury and Venus, are much higher in the sky at some times than others. The best times to see Mercury, if you live in the Northern Hemisphere, are March or April evenings and October or November mornings.

This year, Mercury reaches greatest western elongation from the sun on Saturday (Nov. 1). This means that Mercury is as far as it can get in a westward direction from the sun as it rises over the eastern horizon. I’ve found the best time to spot Mercury is about half an hour before sunrise.

The easiest way to find Mercury is to sweep just above the horizon with binoculars. The brightest star on the eastern horizon will be Arcturus. Mercury will be below Arcturus and well to its right. Once spotted in binoculars, you should have no trouble locating it with your unaided eyes.

If you point a tracking telescope on Mercury, you will be able to continue to observe it as it climbs in the sky, followed by the sun. This is the best opportunity to detect the faint markings on Mercury’s surface, which are usually lost because of Mercury’s brilliance and low altitude. Seen higher against a bright sky, these low contrast markings become more evident.

Even so, they will challenge even experienced observers because of Mercury’s small angular size. The best most of us can hope to see in a telescope is Mercury’s phase: like Venus and the moon, Mercury goes through a series of phases. On Saturday, it will look like a miniature "last-quarter moon."

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Ebola Outbreak May Hold Lessons for Handling Samples from Mars

Centers for Disease Control microbiologists are shown in this 2007 photo in the process of suiting up to access the interior of the organization's Biosafety Level-4 (BSL-4) laboratory. Credit: CDC View full size image

Measures taken in the current Ebola outbreak may hold some clues for how to handle samples brought back to Earth from Mars, a place that could potentially host extraterrestrial microbes.

The 1971 sci-fi film "The Andromeda Strain" dramatized the idea of alien organisms infecting the Earth. Based on a novel by Michael Crichton, the film depicts the spread of an alien germ brought back to Earth by a satellite. An elite team of specialists responds, relying on protective hazmat suits, decontamination and disinfection safety levels, and a secret, high-tech underground facility named Wildfire to study and deal with the deadly extraterrestrial organism.

NASA officials have wanted to build and launch a robotic lander that scoops up some Martian samples and returns them to Earth. Similarly, a human expedition to Mars would surely hunt for past or present evidence of life on the Red Planet. Hauling back Martian samples means potentially dealing with biological "hot property," as well as public concern about creepy crawlers from Mars eating away at Earth's biosphere. [The Search for Life on Mars (A Photo Timelinractice

"While the Ebola situation bears no resemblance to a sample-return mission to Mars, there is a concern that the public could link the two if not properly informed," said John Rummel, a professor of biology at East Carolina University in Greenville, North Carolina.

NASA has long studied the idea of robotically rocketing samples of Mars back to Earth.
Credit: NASA/JPL

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Rummel is a former chair of the Panel on Planetary Protection of the International Council for Science's Committee on Space Research (COSPAR), and is a member of the NASA Advisory Council's Planetary Protection Subcommittee.

Rummel told Space.com that a Mars sample would be contained from the time it leaves Mars until it is proven not to pose a biohazard threat.

"Even more important than the containment facility in which the testing will be done is the fact that scientists will 'practice, practice, practice' to ensure that the sample is contained until shown to be safe for release," Rummel said.

False negatives

The "very tragic set of events" of the current Ebola outbreak may indeed raise public fears about handling potentially infected samples, said Catharine Conley, Planetary Protection Officer at NASA Headquarters in Washington DC.

"In that context," Conley said, "it is true that the greater public awareness of issues related to hazardous materials not being contained properly, and particularly the unfortunate examples of false negatives — like the person not appearing to be sick when he got off the plane in Dallas — do make it easier to communicate similar concerns in the area of planetary protection."

Future Mars expeditions will surely search for evidence of past life on the Red Planet, even potentially identifying organisms that are alive and well on that distant world.
Credit: NASA/JSC

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The current outbreak also highlights "the need to have good protocols in place prior to bringing potentially hazardous materials back to Earth, and having a very careful and well-tested plan for how to determine that they are 'safe,'" Conley told Space.com.

"This is something planetary protection has been working on for quite a while now … but recent events demonstrate how important it is for Earth safety to avoid false negatives, as well as avoiding false positives to protect human activities at Mars," Conley said.

Mass reaction

"I see many issues that we know are a problem being illustrated by the mass reaction, kerfuffle, and misinformation and misunderstanding surrounding Ebola," said Penelope Boston, an astrobiologist and director of the Cave and Karst Studies Program at the New Mexico Institute of Mining and Technology in Socorro.

Boston is a geomicrobiologist and astrobiologist with more than 35 years experience.

"If I were personally going to deal with an agent like Ebola I would go train for six months at a Biosafety Level 4 (BSL-4) containment facility before I trusted myself to work with the virus," Boston said. "I would always have a safety officer bird-dogging my every movement — the buddy system — that is employed in so many hazardous military and civilian contexts," she said. 

Safety procedures

When going into dangerous and potentially deadly environments, like the sulfuric acid cave in Tabasco, situated in southern Mexico, Boston said, a dedicated safety monitor is part of the exploration team.

Genesis solar wind sample curators at NASA's Johnson Space Center handle collectors in the ultraclean Genesis cleanroom. Curators wore suits to keep the collectors clean. The wearer's body is totally enclosed, and exhaled air is filtered through a HEPA filter, seen on the rear side belt. Genesis samples are the first extraterrestrial materials returned to Earth by NASA since the Apollo program, which ended in the early 1970s.
Credit: NASA/JSC

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"That's because no person can both keep their mind on the intensive scientific work they are doing and be absolutely assured of their own adherence to very fussy safety procedures," Boston told Space.com.

"And of course, with spacecraft, we also have the issue of organic chemical cleanliness to deal with, because that could seriously affect the results of highly sensitive life-detection experiments," Boston said. "So the space exploration case is a double-whammy that we are developing protocols to deal with."

Quarantine and containment

Bringing organisms back to Earth from space was spotlighted in the 1971 sci-fi movie, "The Andromeda Strain." The film depicts the spread of an alien germ transported back to Earth by a "Project Scoop" satellite.
Credit: Universal Pictures

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The Center for Disease Control (CDC) has guidelines for all types of biological pathogens, and NASA has worked with the health agency in planning for Mars, said Margaret Race, a senior research scientist at the SETI Institute in Mountain View, California.

Race focuses on the scientific, technical, legal and societal issues of ensuring that missions to the Red Planet and other solar system bodies do not either inadvertently bring Earth microbes to Mars, which would complicate the search for indigenous extraterrestrial life, or return any microbes to Earth. [Mars Myths and Misconceptions: A Quiz]

The CDC has designated different levels of containment. The most virulent agents are kept in Biosafety Level 4 (BSL-4) and have "special" protocols.

"The CDC generally works with known pathogens, but also oversees all types," Race said. "If in doubt, keep it contained and continue to study it," she told Space.com. "Quarantine and containment requirements are updated as needed, for example in response to things like Ebola."

NASA developed its draft Mars sample handling and testing protocols in coordination with experts from CDC and other regulatory agencies, Race said.

Red Planet protocols

NASA's protocols for Mars samples will take into account both safety and scientific accuracy, Race said.

"Clearly, science considerations also apply," she said. "According to studies by the U.S. National Research Council, the risks of Mars sample returnmaterials are deemed very low, but not zero."

Ebola virus
Credit: Frederick A. Murphy/CDC

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NASA will take a deliberately conservative view in handling pristine returned Martian materials, Race aid. This is both for planetary protection considerations, as noted in Outer Space Treaty requirements that are promulgated by COSPAR, and to protect the scientific integrity of the samples.

"Protocols will be updated well in advance of any sample return mission from Mars. There's already a comprehensive process of review and integration of planetary protection requirements that has been endorsed for implementation well in advance of any sample return mission," Race emphasized.

"Obviously, any Mars sample return plans will comply with the most up-to-date CDC and other requirements," Race concluded.

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