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Asample-return mission is aspacecraft mission to collect and return samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as loose material and rocks. These samples may be obtained in a number of ways, such as soil and rock excavation or a collector array used for capturing particles of solar wind or cometary debris. Nonetheless, concerns have been raised that the return of such samples to planet Earth may endanger Earth itself.[1]
To date, samples ofMoon rock from Earth'sMoon have been collected by robotic and crewed missions; the cometWild 2 and the asteroids25143 Itokawa,162173 Ryugu, and101955 Bennu have been visited by robotic spacecraft which returned samples to Earth; and samples of thesolar wind have been returned by the roboticGenesis mission.
In addition to sample-return missions, samples from three identified non-terrestrial bodies have been collected by other means: samples from the Moon in the form ofLunar meteorites, samples fromMars in the form ofMartian meteorites, and samples fromVesta in the form ofHED meteorites.
Samples available on Earth can be analyzed inlaboratories, so we can further our understanding and knowledge as part of thediscovery and exploration of the Solar System. Until now, many important scientific discoveries about theSolar System were made remotely withtelescopes, and some Solar System bodies were visited by orbiting or even landing spacecraft with instruments capable ofremote sensing or sample analysis. While such an investigation of the Solar System is technically easier than a sample-return mission, the scientific tools available on Earth to study such samples are far more advanced and diverse than those that can go on spacecraft. Further, analysis of samples on Earth allows follow up of any findings with different tools, including tools that can tell intrinsic extraterrestrial material from terrestrial contamination,[2] and those that have yet to be developed; in contrast, a spacecraft can carry only a limited set of analytic tools, and these have to be chosen and built long before launch.
Samples analyzed on Earth can be matched against findings of remote sensing for more insight into theprocesses that formed the Solar System. This was done, for example, with findings by theDawn spacecraft, which visited the asteroid Vesta from 2011 to 2012 for imaging, and samples fromHED meteorites (collected on Earth until then), which were compared to data gathered by Dawn.[3] These meteorites could then be identified as material ejected from the large impact craterRheasilvia on Vesta. This allowed deducing the composition of the crust,mantle and core of Vesta. Similarly, somedifferences in the composition of asteroids (and, to a lesser extent, different compositions ofcomets) can be discerned by imaging alone. However, for a more precise inventory of the material on these different bodies, more samples will be collected and returned in the future, to match their compositions with the data gathered through telescopes andastronomical spectroscopy.
One further focus of such investigation—besides the basic composition andgeologic history of the various Solar System bodies—is the presence of thebuilding blocks of life on comets, asteroids,Mars or the moons of thegas giants. Several sample-return missions to asteroids and comets are currently in the works. More samples from asteroids and comets will help determine whether life formed in space and was carried to Earth by meteorites. Another question under investigation is whetherextraterrestrial life formed on other Solar System bodies like Mars or onthe moons of the gas giants, and whether life might even exist there. The result of NASA's last "Decadal Survey" was to prioritize a Mars sample-return mission, as Mars has a special importance: it is comparatively "nearby", might have harbored life in the past, and might even continue to sustain life.Jupiter's moonEuropa is another important focus in the search for life in the Solar System. However, due to the distance and other constraints, Europa might not be the target of a sample-return mission in the foreseeable future.
Planetary protection aims to prevent biological contamination of both the targetcelestial body and theEarth in the case of sample-return missions. A sample return from Mars or other location with the potential to host life is acategory V mission under COSPAR, which directs to the containment of any unsterilized sample returned to Earth. This is because it is unknown what the effects such hypothetical life would be on humans or thebiosphere of Earth.[4] For this reason,Carl Sagan andJoshua Lederberg argued in the 1970s that we should do sample-return missions classified as category V missions with extreme caution, and later studies by the NRC and ESF agreed.[4][5][6][7][8]
In July 1969,Apollo 11 achieved the first successful sample return from another Solar System body when it returned 22 kilograms (49 lb) of Lunar surface material. This was followed by 34 kilograms (75 lb) of material andSurveyor 3parts fromApollo 12, 42.8 kilograms (94 lb) of material fromApollo 14, 76.7 kilograms (169 lb) of material fromApollo 15, 94.3 kilograms (208 lb) of material fromApollo 16, and 110.4 kilograms (243 lb) of material fromApollo 17.[citation needed] TheApollo program as a whole returned over 382 kg (842 lb) oflunar rocks andregolith, includinglunar soil, to theLunar Receiving Laboratory inHouston.[9][10][11] Today, 75% of the samples are stored at theLunar Sample Laboratory Facility built in 1979.[12]
In 1970, the roboticSoviet missionLuna 16 returned 101 grams (3.6 oz) of lunar soil, followed byLuna 20's return of 55 grams (1.9 oz) in 1974, andLuna 24's return of 170 grams (6.0 oz) in 1976. Although they recovered far less than the Apollo missions, they did this fully automatically. Apart from these three successes, other attempts under theLuna programme failed. The first two missions were intended to compete with Apollo 11 and were undertaken shortly before it in June and July 1969.Luna E-8-5 No. 402 failed at start, andLuna 15 crashed on the Moon. Later, other sample-return missions failed:Kosmos 300 andKosmos 305 in 1969,Luna E-8-5 No. 405 in 1970,Luna E-8-5M No. 412 in 1975 had unsuccessful launches, andLuna 18 in 1971 andLuna 23 in 1974 had unsuccessful landings on the Moon.[13]
In 1970, the Soviet Union planned for a 1975 firstMars sample-return mission in theMars 5NM project. This mission was planned to use anN1 rocket, but this rocket never flew successfully and the mission evolved into theMars 5M project, which would use a double launch with the smallerProton rocket and an assembly at aSalyut space station. This Mars 5M mission was planned for 1979, but was canceled in 1977 due to technical problems and complexity.[14]
The Orbital Debris Collection (ODC) experiment deployed on theMir space station for 18 months in 1996–97 usedaerogel to capture particles from low Earth orbit, including both interplanetary dust and man-made particles.[15]
The next mission to return extraterrestrial samples was theGenesis mission, which returned solar wind samples to Earth from beyond Earth orbit in 2004. Unfortunately, theGenesis capsule failed to open its parachute while re-entering the Earth's atmosphere and crash-landed in the Utah desert. There were fears of severe contamination or even total mission loss, but scientists managed to save many of the samples. They were the first to be collected from beyond lunar orbit.Genesis used a collector array made of wafers of ultra-puresilicon,gold,sapphire, anddiamond. Each different wafer was used to collect a different part of thesolar wind.[16]
Genesis was followed byNASA'sStardust spacecraft, which returned comet samples to Earth on 15 January 2006. It safely passed byComet Wild 2 and collected dust samples from the comet'scoma while imaging the comet's nucleus.Stardust used a collector array made of low-density aerogel (99% of which is space), which has about 1/1000 of the density of glass. This enables the collection of cometary particles without damaging them due to high impact velocities. Particle collisions with even slightly porous solid collectors would result in the destruction of those particles and damage to the collection apparatus. During the cruise, the array collected at least seven interstellar dust particles.[17]
In June 2010 theJapan Aerospace Exploration Agency (JAXA)Hayabusa probe returned asteroid samples to Earth after a rendezvous with (and a landing on)S-type asteroid25143 Itokawa. In November 2010, scientists at the agency confirmed that, despite failure of the sampling device, the probe retrieved micrograms of dust from the asteroid, the first brought back to Earth in pristine condition.[18]
The RussianFobos-Grunt was a failed sample-return mission designed to return samples fromPhobos, one of the moons of Mars. It was launched on 8 November 2011, but failed to leave Earth orbit and crashed after several weeks into the southern Pacific Ocean.[19][20]
TheJapan Aerospace Exploration Agency (JAXA) launched the improvedHayabusa2 space probe on 3 December 2014.Hayabusa2 arrived at the targetnear-EarthC-type asteroid162173 Ryugu (previously designated1999 JU3) on 27 June 2018.[21] It surveyed the asteroid for a year and a half and took samples. It left the asteroid in November 2019[22][23] and returned to Earth on 6 December 2020.[24]
TheOSIRIS-REx mission was launched in September 2016 on a mission to return samples from the asteroid101955 Bennu.[25][26] The samples are expected to enable scientists to learn more about the time before the birth of the Solar System, initial stages of planet formation, and the source of organic compounds that led to the formation of life.[27] It reached the proximity of Bennu on 3 December 2018,[28] where it began analyzing its surface for a target sample area over the next several months. It collected its sample on 20 October 2020,[29][30] and landed back on Earth again on 24 September 2023, making OSIRIS-REx the fifth successful sample return mission for mankind, in its return of samples from an extra-terrestrial body.[31][32][33][34] Shortly after the sample container was retrieved and transferred to an "airtight chamber at theJohnson Space Center in Houston, Texas", the lid on the container was opened. Scientists commented that they "found black dust and debris on the avionics deck of the OSIRIS-REx science canister" on the initial opening. Later study was planned. On 11 October 2023, the recovered capsule was opened to reveal a "first look" at the asteroid sample contents.[35][36] On 13 December 2023, further studies of the returned sample were reported and revealedorganic molecules as well as unknown materials which require more study to have a better idea of their composition and makeup.[37][38] On 13 January 2024, NASA reported finally fully opening, after three months of trying, the recovered container with samples from the Bennu asteroid.[39][40] The total weight of the recovered material weighed 121.6 g (4.29 oz), over twice the mission's goal.[41]
China'sCNSA launched theChang'e 5 and6 lunar sample-return mission on 23 November 2020 and 3 May 2024 respectively, which returned to Earth with 2 kilograms of lunar soil each on 16 December 2020 and 25 June 2024 respectively.[42] These were the first lunar sample-return missions in over 40 years.[43] The Chang'e 6 mission, which landed in theApollo crater basin in the southern hemisphere of the lunar far side, was the first to retrieve samples from thefar side of the Moon, as all previous collective lunar samples having been collected from thenear side.[44]
CNSA is planning a mission calledTianwen-2 to return samples from469219 Kamoʻoalewa which is planned to launch in 2025.[45] CNSA plans for a Mars sample return mission by 2030.[46][47] Also, theChinese Space Agency is designing a sample-retrieval mission fromCeres that would take place during the 2020s.[48]
JAXA is developing theMMX mission, a sample-return mission toPhobos that will be launched in 2026.[49] MMX will study bothmoons of Mars, but the landing and the sample collection will be on Phobos. This selection was made because of the two moons, Phobos's orbit is closer to Mars and its surface may have particles blasted from Mars. Thus the sample may contain material originating on Mars itself.[50] A propulsion module carrying the sample is expected to return to Earth in 2031.[49]
NASA andESA have long planned aMars Sample-Return Mission.[51] ThePerseverance rover, deployed in 2020, is collecting drill core samples and stashing them on the Mars surface.[52] As of September 2023, it has gathered one atmospheric sample and 8 igneous rock samples, 11sedimentary rock samples and a pair of regolith samples.[53] On 22 November 2023, NASA announced that it was cutting back on the Mars sample-return mission due to a shortage of funds.[54] In January 2024, the proposed NASA plan was challenged due to budget and scheduling considerations, and investigation into alternate plans begun.[55]
Russia has plans forLuna-Glob missions to return samples from the Moon by 2027 andMars-Grunt to return samples from Mars in the late 2020s.[citation needed]
Sample-return methods include, but are not restricted to the following:
A collector array may be used to collect millions or billions of atoms, molecules, and fine particulates by using wafers made of different elements. The molecular structure of these wafers allows the collection of various sizes of particles. Collector arrays, such as those flown onGenesis, are ultra-pure in order to ensure maximal collection efficiency, durability, and analytical distinguishability.[citation needed]
Collector arrays are useful for collecting tiny, fast-moving atoms such as those expelled by the Sun through the solar wind, but can also be used for collection of larger particles such as those found in the coma of a comet. The NASA spacecraft known asStardust implemented this technique. However, due to the high speeds and size of the particles that make up the coma and the area nearby, a dense solid-state collector array was not viable. As a result, another means for collecting samples had to be designed to preserve the safety of the spacecraft and the samples themselves.[citation needed]
Aerogel is asilica-based porous solid with a sponge-like structure, 99.8% of whose volume is empty space. Aerogel has about 1/1000 of the density of glass. An aerogel was used in theStardust spacecraft because the dust particles the spacecraft was to collect would have an impact speed of about 6 km/s. A collision with a dense solid at that speed could alter their chemical composition or vaporize them completely.[56]
Since the aerogel is mostly transparent, and the particles leave a carrot-shaped path once they penetrate the surface, scientists can easily find and retrieve them. Since its pores are on thenanometer scale, particles, even ones smaller than a grain of sand, do not merely pass through the aerogel completely. Instead, they slow to a stop and then are embedded within it. TheStardust spacecraft has a tennis-racket-shaped collector with aerogel fitted to it. The collector is retracted into its capsule for safe storage and delivery back to Earth. Aerogel is quite strong and easily survives both launching and space environments.[56]
Some of the riskiest and most difficult types of sample-return missions are those that require landing on an extraterrestrial body such as an asteroid, moon, or planet. It takes a great deal of time, money, and technical ability to even initiate such plans. It is a difficult feat that requires that everything from launch to landing to retrieval and launch back to Earth is planned out with high precision and accuracy.[citation needed]
This type of sample return, although having the most risks, is the most rewarding forplanetary science. Furthermore, such missions carry a great deal of public outreach potential, which is an important attribute forspace exploration when it comes to public support. The only successful robotic sample-return missions of this type have been SovietLuna and ChineseChang'e lunar landers. While other missions collected materials from asteroids by various means, they did so without "landing", given their very low gravity.[citation needed]
| Launch date | Operator | Name | Sample origin | Samples returned | Recovery date | Mission result |
|---|---|---|---|---|---|---|
| 16 July 1969 |  United States | Apollo 11 | Moon | 22 kilograms (49 lb) | 24 July 1969 | Success |
| 14 November 1969 | United States | Apollo 12 | Moon | 34 kilograms (75 lb) andSurveyor 3parts[note 1][57] | 24 November 1969 | Success |
| 11 April 1970 | United States | Apollo 13 | Moon | — | 17 April 1970 | Failure |
| 31 January 1971 | United States | Apollo 14 | Moon | 43 kilograms (95 lb) | 9 February 1971 | Success |
| 26 July 1971 | United States | Apollo 15 | Moon | 77 kilograms (170 lb) | 7 August 1971 | Success |
| 16 April 1972 | United States | Apollo 16 | Moon | 95 kilograms (209 lb) | 27 April 1972 | Success |
| 7 December 1972 | United States | Apollo 17 | Moon | 111 kilograms (245 lb) | 19 December 1972 | Success |
| 22 March 1996 |  Russia | Earth-Orbital Debris Collection | Low Earth orbit | Particles | 6 October 1997 | Success[58] |
| 14 April 2015 |  Japan | Tanpopo mission | Low Earth orbit | Particles | February 2018[59] | Success |
| Launch date | Operator | Name | Sample origin | Samples returned | Recovery date | Mission result |
|---|---|---|---|---|---|---|
| 14 June 1969 |  Soviet Union | Luna E-8-5 No. 402 | Moon | — | — | Failure |
| 13 July 1969 | Soviet Union | Luna 15 | Moon | — | — | Failure |
| 23 September 1969 | Soviet Union | Kosmos 300 | Moon | — | — | Failure |
| 22 October 1969 | Soviet Union | Kosmos 305 | Moon | — | — | Failure |
| 6 February 1970[13] | Soviet Union | Luna E-8-5 No. 405 | Moon | — | — | Failure |
| 12 September 1970 | Soviet Union | Luna 16 | Moon | 101 grams (3.6 oz) | 24 September 1970 | Success |
| 2 September 1971 | Soviet Union | Luna 18 | Moon | — | — | Failure |
| 14 February 1972 | Soviet Union | Luna 20 | Moon | 55 grams (1.9 oz) | 25 February 1972 | Success |
| 2 November 1974 | Soviet Union | Luna 23 | Moon | — | — | Failure |
| 16 October 1975 | Soviet Union | Luna E-8-5M No. 412 | Moon | — | — | Failure |
| 9 August 1976 | Soviet Union | Luna 24 | Moon | 170 grams (6.0 oz) | 22 August 1976 | Success |
| 7 February 1999 | United States | Stardust | 81P/Wild | Particles, weighing approx 1 gram (0.035 oz) | 15 January 2006 | Success |
| 8 August 2001 | United States | Genesis | Solar wind | Particles | 9 September 2004 | Partial success |
| 9 May 2003 | Japan | Hayabusa | 25143 Itokawa | Particles, weighing less than 1 gram (0.035 oz) | 13 June 2010 | Partial success |
| 8 November 2011 | Russia | Fobos-Grunt | Phobos | — | — | Failure |
| 3 December 2014 | Japan | Hayabusa2 | 162173 Ryugu | 5.4 grams (0.19 oz)[60] (including gas samples) | 6 December 2020 | Success |
| 8 September 2016 | United States | OSIRIS-REx | 101955 Bennu | 121.6 grams (4.29 oz)[36][61] | 24 September 2023 | Success |
| 23 November 2020 |  China | Chang'e 5 | Moon | 1,731 grams (61.1 oz) | 16 December 2020 | Success |
| 3 May 2024 | China | Chang'e 6 | Moon | 1,935.3 grams (68.27 oz)[62] | 25 June 2024 | Success |
| 2025 | China | Tianwen-2 | 469219 Kamoʻoalewa | — | 2027 | Planned[63] |
| 2026 | Japan | MMX | Phobos | — | 2031 | Planned |
| 2028 | United States / European Space Agency | NASA-ESA Mars Sample Return | Mars | 500 grams (18 oz) [note 2][64] | 2033 | Ongoing[note 3] |
| 2028 |  India | Chandrayaan-4 | Moon | — | 2028 | Planned |
| 2028 | China | Tianwen-3 | Mars | — | 2031 | Planned[65] |
A total of 382 kilograms of lunar material, comprising 2200 individual specimens returned from the Moon...
