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We have satellites and telescopes looking outward and inward to the earth. Would any of these detect an extraterrestrial spacecraft before it landed, or in other words, would we know a spacecraft was approaching before it did (assuming its going at some reasonably detectable speed in our local area)?
Let's assume it is Saturn V like wrt detectability.
Some thoughts about Earth-based detection systems:
We are looking at asteroids using radar: For instance the former Arecibo telescope could actively send out radio waves and calculate object position and size. However, we might be able to detect an incoming spaceship using this technology, assuming that the object approaches Earth within the radio beam, if we we are currently studying another object. In other words: Detecting an incoming object would be purely chance.
An all sky camera network for meteorite detection is another outward-looking system worth mentioning, but that would be very very briefly before landing of a hypothetical extraterrestrial space ship. I am sure you are not after this option since we would be seeing the object already with naked eyes if it would not be incoming at a very remote location. However, this option is to my knowledge working 365/24/7 and covers large portions of the sky, I believe.
Edit suggested by uhoh: There are also initiatives like NASA's Space Fence or ESA's Space Surveillance and Tracking (SST) segment monitoring space debris within the geospace which could possibly detect other objects as well, see also https://space.stackexchange.com/q/45144/12102
Concerning satellite-based observations: If the objects emits significant radiation e.g. in parts of the spectrum of communication satellites, we might detect anomalities or malfunctions in one or more satellire and by chance figure out the extraterrestrial source of the distortion. This would of course only hold for slow approaching objects.
So NASA recently re-detected the upper stage of a old centaur rocket from Surveyor 2 identified as NEO 2020 SOO. Now, there was some advantages with this object as people had noticed it before so spent some time working out its orbit and where it would be. But it suggests we can find and observe objects smaller than a Saturn V a long time before they reach the atmosphere. Wikipedia says its closest approach was 50,000 km so that gives a lower limit for finding a spacecraft before it lands on Earth, but the actual distance when we first saw it was proper alot further.
China says it has launched and landed a reusable spacecraft
A launch of the Long March 2F rocket similar to the one that took the reusable spacecraft into orbit this past on September 4. Lintao Zhang/Getty Images
On September 6, China successfully landed a reusable spacecraft the country had launched into orbit just two days before, according to the state-run Xinhua News Agency. “The successful flight marked the country’s important breakthrough in reusable spacecraft research and is expected to offer convenient and low-cost round trip transport for the peaceful use of the space,” Xinhua reported.
What we know: The country has provided very few specific details into what the mission was and the spacecraft that was tested. The spacecraft was launched from Jiuquan Satellite Center in the Gobi Desert, from a Long March 2F rocket. No images were released.
Spaceplane speculation: China has previously expressed interest in developing reusable spaceflight architecture. A Xinhua report three years ago suggested the country would actually launch such a spacecraft this year—one that was distinct from “traditional one-off spacecraft” and would “fly into the sky like an aircraft.”
That report led many experts to believe China wanted to develop its own version of the US Air Force’s X-37B spaceplane, which is capable of flying in low Earth orbit for several years on end before returning to Earth and landing horizontally on a runway. A Chinese military source told the South China Morning Post that “maybe you can take a look at the US X-37B [spaceplane]” as a hint for what the Chinese spacecraft looks like.
That speculation was bolstered by the fact that China made visual modifications to the launch tower for this mission, possibly to accommodate a payload that is wider in diameter (and more like a spaceplane).
An additional wrinkle: According to SpaceNews, US space surveillance identified an additional smaller object released into orbit by the Chinese spacecraft before its return to Earth. It’s not yet clear what this object is and what its purpose might be.
More to come: This is likely just the first in a series of new tests of reusable spacecraft to stream out of China over the next few years. The China Aerospace Science and Industry Corp. (CASIC) is working on its own spaceplane named Tengyun. And the private company iSpace previously suggested it wanted to develop a spaceplane of its own.
By using different technologies, astronomers are able to build these spacecrafts to gain a better understanding of these bodies around us. However, some of these spacecrafts were not successful. The spacecrafts that were successful provided astronomers with valuable information and detailed pictures.
Each spacecraft had a destination and a duty to perform. According to documentation, spacecrafts have landed and sent information from the moon, jupiter, venus, camets, saturn's moon, asteroids, and mars. The data that was received from these machines ranged from pictures to an in-depth analysis of the substances that make up the planet.
Numerous spacecrafts have landed and flew by Earth’s Moon since the year of 1958. Many of these spacecrafts were launched from the United States, being followed by the USSR with the lunar series. The USA released Pioneer zero, one, three, and four to fly by and orbit the moon. However, it was the USSR who created the first spacecraft, Luna, which landed on the moon September twelfth of 1959. Overall, the USSR landed a spacecraft on the moon about fourteen times. The United States have four programs that are used for the purpose of the moon: Ranger, American Surveyors, Apollo, and Discovery Program. The first spacecraft landing was on January 26 th of 1962 by the spacecraft Ranger.
After approximately 50 years later, Japan made its first landing on the moon with the Hiten Series. They were followed by ESA (European Space Agency) with the Smart series spacecraft. These spacecraft landings gave scientists valuable information regarding the moon. They discovered craters ice on the north and south poles, and water vapors was not present.
Next, spacecrafts have landed or flew by the second planet from the sun Venus. Venus has acid rain and a pressure 92 times greater than the earth. Therefore, the spacecrafts that approaches Vens must be sturdy, which is shown with the USSR spacecraft, Venera. On June eight and fourteenth of 1975, Venera nine and ten landed on Venus. Another series called Vega, were spacecrafts mainly used to fly by Venus. On the other hand, the United States made one landing on Venus, in comparison to the USSR fourteen landings. The Pioneer Series transmitted signals for 67 minutes and one of the four atmospheric probes survived. Important Information about Venus was discovered from the spacecrafts. Venus’ atmosphere is made up of carbon dioxide, the surface is 875 degrees Fahrenheit, volcanoes were present, the water evaporated, and is now contained in the clouds causing acid rain.
The Viking, Sojourner, and Mars Programs are US programs used for spacecraft exploration of the fourth planet, Mars. The spacecraft Marines was the first launch of a Mars fly by spacecraft in February o f 1969. It was not until the time of 1973 when the United States released Viking in August as a Mars orbiter and a having a successful landing. The USSR also had a Mars program landing the first spacecraft in history on the planet Mars on May 19 th in 1971. The total landings for the United States are six and three were made by the USSR. The information that was discovered about Mars was that at one point it was drenched with water, may have sustained life, and it’s year is 687 Earth Days.
The asteroid Eros was the next place of landing for the United States. February twelfth of 2001, the NEAR spacecraft made a controlled landing onto the asteroids surface. After a four year journey and one year of orbiting Eros, the spacecraft landed. The spacecraft used laser radar to measure the asteroid Eros. In conclusion, Eros is the second largest near earth asteroid.
Another spacecraft landing done only by the United States was to Jupiter. They were successful in sending six spacecrafts to Jupiter since 1973: the Pioneer Series, Voyager SEries, Galileo, and Ulysses. Some probes flew around Jupiter sending back images of the planet specifically, the Great Red Spot. It was found that Jupiter's radiation by the belt affected the probes around the planet. The magnetic field of Jupiter is very large in comparison to other magnetic fields of our solar system. The atmosphere of Jupiter is thick and contains both hydrogen and helium.
The European Space Agency, or ESA, launched the Cassini-Huygens Probe to land on Saturn's largest moon, Titan. On January 14th of 2005, the probe landed successfully on Titan suppling scientists with pictures and information regarding the surface of Titan. The surface temperature is about -248 degrees Fahrenheit and that Titan has an atmosphere. Scientists consider Titan one of the most interesting bodies in our solar system. It is larger than both Pluto and Mercury, and believed to have methane lakes and other chemicals.
The spacecrafts that have visited other planets has opened more doors for the exploration of our solar system. These probes bought or transmitted valuable information concerning that planet that can be used to develop and support theories. They give scientists a better understanding of the components of a planet, moon, or asteroid.
Beginning with Luna 2 in 1959, the first few spacecraft to reach the lunar surface were impactors, not landers. They were part of the Soviet Luna program or the American Ranger program.
In 1966, the Soviet Luna 9 became the first spacecraft to achieve a lunar soft landing and to transmit photographic data to Earth. The American Surveyor program (1966–1968) was designed to determine where Apollo could land safely. As a result, these robotic missions required soft landers to sample the lunar soil and determine the thickness of the dust layer, which was unknown before Surveyor.
The U.S.-crewed Apollo Lunar Modules (1969–1972) with rovers (1971–1972) and late Soviet large robotic landers (1969–), Lunokhods (1970–1973) and sample return missions (1970–1976) used a rocket descent engine for a soft landing of astronauts and lunar rovers on the Moon.
The Altair spacecraft, previously known as the "Lunar Surface Access Module" or "LSAM", was the planned lander for the Constellation program prior to the cancellation of Project Constellation.
As of August 2012 [update] NASA is developing vehicles that use a rocket descent engine permitting them to land on the Moon and other locations. These vehicles include the Mighty Eagle lander and the Morpheus lander. The Project Morpheus lander may have sufficient thrust to propel a crewed ascent stage.
Russia has plans for the Luna-Grunt mission to return samples from the Moon by 2021.
The Chinese Chang'e 3 mission and its Yutu ('Jade Rabbit') rover landed on 14 December 2013. In 2019, China's Chang'e 4 mission successfully landed the Yutu-2 rover on the far side of the Moon.  Chang'e 5 and Chang'e 6 are designed to be sample return missions.  Chang'e 5 is currently scheduled for 2020, while Chang'e 6 is planned for 2023  or 2024.  Chang'e 5 mission landed on the Moon on 1 December 2020, China completed the Chang'e 5 mission on 16 December 2020 with the return of approximately 2 kilograms of lunar sample.
Lander Vikram on Chandrayaan-2, a maiden soft landing effort by the Indian Space Research Organization, lost contact to control on 6 September 2019, some minutes before landing. [ citation needed ]
The Soviet Venera program included a number of Venus landers, some of which were crushed during descent much as Galileo's Jupiter "lander" and others which successfully touched down. Venera 3 in 1966 and Venera 7 in 1970 became the first impact and soft landing on Venus respectively. The Soviet Vega program also placed two balloons in the Venusian atmosphere in 1985, which were the first aerial tools on other planets.
The Soviet Union's Mars 1962B became the first Earth-based mission intended to impact on Mars in 1962. In 1971, the lander of the Mars 3 probe conducted the first soft landing on Mars, but communication was lost within a minute after touchdown, which occurred during one of the worst global dust storms since the beginning of telescopic observations of the Red Planet. Three other landers, Mars 2 in 1971 and Mars 5 and Mars 6 in 1973, either crashed or failed to even enter the planet's atmosphere. All four landers used an aeroshell-like heat shield during atmospheric entry. Mars 2 and Mars 3 landers carried the first small skis-walking Mars rovers that did not work on the planet.
The Soviet Union planned the heavy Marsokhod Mars 4NM mission in 1973 and the Mars sample return Mars 5NM mission in 1975, but neither occurred due to needing the N1 super-launcher that was never flown successfully. A double-launching Soviet Mars 5M (Mars-79) sample return mission was planned for 1979 but cancelled due to complexity and technical problems.
Viking 1 and Viking 2 were launched respectively in August and September 1975, each comprising an orbiter vehicle and a lander. Viking 1 landed in July 1976 and Viking 2 in September 1976. The Viking program rovers were the first successful, functioning Mars landers. The mission ended in May 1983, after both landers had died.
In the 1970s, the US planned the Voyager-Mars mission. This would have consisted of two orbiters and two landers, launched by a single Saturn V rocket, but the mission was cancelled.
Mars 96 was the first complex post-Soviet Russian mission with an orbiter, lander, and penetrators. Planned for 1996, it failed at launch. A planned repeat of this mission, Mars 98, was cancelled due to lack of funding.
The U.S. Mars Pathfinder was launched in December 1996 and released the first acting rover on Mars, named Sojourner, in July 1997. It failed in September 1997, probably due to electronics failure caused by the cold temperatures. Mars Pathfinder was part of the canceled Mars Environmental Survey program with a set of 16 landers planned for 1999–2009.
The Mars Polar Lander ceased communication on 3 December 1999 prior to reaching the surface and is presumed to have crashed.
The European Beagle 2 lander deployed successfully from the Mars Express spacecraft but the signal confirming a landing which should have come on 25 December 2003 was not received. No communication was ever established and Beagle 2 was declared lost on 6 February 2004. The proposed 2009 British Beagle 3 lander mission to search for life, past or present, was not adopted.
The French/ESA NetLander mission for 2007 or 2009, with an orbiter and 4 landers, was canceled because it was too expensive. Its successor, a multi-lander mission for 2011–2019 called Mars MetNet, was not adopted by the ESA.
The American Mars Exploration Rovers Spirit and Opportunity were launched in June and July 2003. They reached the Martian surface in January 2004 using landers featuring airbags and parachutes to soften impact. Spirit ceased functioning in 2010, more than five years past its design lifetime.  As of 13 February 2017, Opportunity was declared effectively dead, having exceeded its three-month design lifetime by well over a decade. 
The U.S. spacecraft Phoenix successfully achieved soft landing on the surface of Mars on 25 May 2008, using a combination of parachutes and rocket descent engines.
Mars Science Laboratory, which carried the rover Curiosity, was successfully launched by NASA on 26 November 2011. It landed in the Aeolis Palus region of Gale Crater on Mars on 6 August 2012.
The China launched the Tianwen-1 mission, in 23 July 2020. It includes an orbiter, a lander and a 240 kilograms rover.The orbiter was placed into orbit on 10 February 2021. The Zhurong successfully soft landed on 14 May 2021 and deployed on 22 May 2021 and dropped a remote camera on Mars on 1 June, 2021.
Exploration of Mars including the use of landers continues to this day. Amongst them, Russia has planned a Mars sample return mission Mars-Grunt for around 2026.
Martian moons Edit
While several flybys conducted by Mars orbiting probes have provided images and other data about the Martian moons Phobos and Deimos, only few of them intended to land on the surface of these satellites. Two probes under the Soviet Phobos program were successfully launched in 1988, but in 1989 the intended landings on Phobos and Deimos were not conducted due to failures in the spacecraft system. The post-Soviet Russian Fobos-Grunt probe was an intended sample return mission to Phobos in 2012 but failed after launch in 2011.
In 2007 European Space Agency and EADS Astrium proposed and developed the mission to Phobos to 2016 with lander and sample return, but it stayed as a project. Since 2007 the Canadian Space Agency has considered a mission to Phobos called Phobos Reconnaissance and International Mars Exploration (PRIME), which would include an orbiter and lander. Recent proposals include a 2008 NASA Glenn Research Center Phobos and Deimos sample return mission, the 2013 Phobos Surveyor, and the OSIRIS-REx II mission concept.
The Japanese Aerospace Exploration Agency (JAXA) plans to launch the Martian Moons Exploration (MMX) mission in 2024, a sample return mission targeting Phobos.  MMX will land and collect samples from Phobos multiple times, along with deploying a rover jointly developed by CNES and the German Aerospace Center (DLR).  By using a corer sampling mechanism, the spacecraft aims to retrieve a minimum of 10 g of samples. MMX will return to Earth in 2029. 
Russia plans to repeat its Fobos-Grunt mission around 2024.
The Huygens probe, carried to Saturn's moon Titan by Cassini, was specifically designed to survive landing on land or on liquid. It was thoroughly drop-tested to make sure it could withstand impact and continue functioning for at least three minutes. However, due to the low-speed impact, it continued providing data for more than two hours after it landed. The landing on Titan in 2005 was the first landing on the planet's satellites outside the Moon.
The proposed U.S. Titan Mare Explorer (TiME) mission considered a lander that would splash down in a lake in Titan's northern hemisphere and float on the surface of the lake for few months. Spain's proposed Titan Lake In-situ Sampling Propelled Explorer (TALISE) mission is similar to the TiME lander but has its own propulsion system for controlling shipping.
Comets and asteroids Edit
Vesta, the multi-aimed Soviet mission, was developed in cooperation with European countries for realization in 1991–1994 but canceled due to the Soviet Union disbanding. It included a flyby of Mars, where Vesta would deliver an aerostat (balloon or airship) and small landers or penetrators, followed by flybys of Ceres or 4 Vesta and some other asteroids with the impact of a large penetrator on one of them. [ clarification needed ]
NASA's canceled Comet Rendezvous Asteroid Flyby mission considered the launch in 1995 and landing of penetrators on a comet's nucleus in 2001.
The first landing on a small Solar System body (an object in the Solar System that is not a moon, planet, or dwarf planet) was performed in 2001 by the probe NEAR Shoemaker at asteroid 433 Eros despite the fact that NEAR was not originally designed to be capable of landing.
The Hayabusa probe made several attempts to land on 25143 Itokawa in 2005 with mixed success, including a failed attempt to deploy a rover. Designed to rendezvous and land on a low-gravity body, Hayabusa became the second spacecraft to land on an asteroid, and in 2010 the first sample return mission from an asteroid.
The Rosetta probe, launched 2 March 2004, put the first robotic lander Philae on the comet Churyumov–Gerasimenko on 12 November 2014. Due to the extremely low gravity of such bodies, the landing system included a harpoon launcher intended to anchor a cable in the comet's surface and pull the lander down.
Japan (JAXA) launched the Hayabusa2 asteroid space probe in 2014 to deliver several landing parts (including Minerva II and German Mobile Asteroid Surface Scout (MASCOT) landers and a Small Carry-on Impactor (SCI) penetrator) in 2018–2019 to return samples to Earth by 2020.
The Chinese Space Agency is designing a sample retrieval mission from Ceres that would take place during the 2020s. 
Launched in October 2018 and expected to reach Mercury in December 2025, ESA's BepiColombo mission to Mercury was originally designed to include the Mercury Surface Element (MSE). The lander would have carried a 7 kg payload consisting of an imaging system (a descent camera and a surface camera), a heat flow and physical properties package, an alpha particle X-ray spectrometer, a magnetometer, a seismometer, a soil penetrating device (mole), and a micro-rover. The MSE aspect of the mission was cancelled in 2003 due to budgetary constraints. 
Moons of Jupiter Edit
A few Jupiter probes provide many images and other data about its moons. Some proposed missions with landing on Jupiter's moons were canceled or not adopted. The small nuclear-powered Europa lander was proposed as part of NASA's Jupiter Icy Moons Orbiter (JIMO) mission that was canceled in 2006.
Currently, the ESA is planning to launch the Jupiter Icy Moon Explorer (JUICE) mission in 2022, which includes the Russian Ganymede Lander making a soft landing on Ganymede around 2033. In addition, NASA offered the ESA the opportunity to design a lander or impactor to fly alongside NASA's proposed orbiter in the Europa Clipper mission planned for 2025. As Europa is hypothesized to have water beneath its icy surface, missions are sent to investigate its habitability and assess its astrobiological potential by confirming the existence of water on the moon and determining the water's characteristics. Despite the high radiation environment around Europa and Jupiter, which would cause issues for robotic surface missions, NASA's Europa Lander mission is still under consideration and there is steady lobbying for future missions. Russia's Laplace-P was proposed to be included as a part of the now-canceled joint NASA/ESA Europa Jupiter System Mission (EJSM)/Laplace mission but remains an option for future missions. Another proposal calls for a large nuclear-powered "melt probe" (cryobot) that would melt through the ice until it reached an ocean below where it would deploy an autonomous underwater vehicle (AUV or "hydrobot") that would gather information.
Deep Space 2 Edit
The Deep Space 2 impactor probe was to be the first spacecraft to penetrate below the surface of another planet. However, the mission failed with the loss of its mother ship, Mars Polar Lander, which lost communication with Earth during entry into Mars' atmosphere on 3 December 1999.
Deep Impact Edit
Comet Tempel 1 was visited by NASA's Deep Impact probe on 4 July 2005. The impact crater formed was approximately 200 m wide and 30–50 m deep, and scientists detected the presence of silicates, carbonates, smectite, amorphous carbon and polycyclic aromatic hydrocarbons.
Moon Impact Probe Edit
The Moon Impact Probe (MIP) developed by the Indian Space Research Organisation (ISRO), India's national space agency, was a lunar probe that was released on 14 November 2008 by ISRO's Chandrayaan-1 lunar remote sensing orbiter. Chandrayaan-1 was launched on 22 October 2008. It led to the discovery of the presence of water on the Moon.  
The Lunar Crater Observation and Sensing Satellite (LCROSS) was a robotic spacecraft operated by NASA to perform a lower-cost means of determining the nature of hydrogen detected at the polar regions of the Moon.  The main LCROSS mission objective was to explore the presence of water ice in a permanently shadowed crater near a lunar polar region.  LCROSS was launched together with the Lunar Reconnaissance Orbiter (LRO) on 18 June 2009, as part of the shared Lunar Precursor Robotic Program. LCROSS was designed to collect and relay data from the impact and debris plume resulting from the launch vehicle's spent Centaur upper rocket stage striking the crater Cabeus near the south pole of the Moon. Centaur impacted successfully on 9 October 2009, at 11:31 UTC. The "shepherding spacecraft" (carrying the LCROSS mission payload)  descended through Centaur's plume of debris, and collected and relayed data before impacting six minutes later at 11:37 UTC. The project was successful in discovering water in Cabeus. 
The NASA MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) mission to Mercury launched on 3 August 2004 and entered orbit around the planet on 18 March 2011. Following a mapping mission, MESSENGER was directed to impact Mercury's surface on 30 April 2015. The spacecraft's impact with Mercury occurred near 3:26 pm EDT on 30 April 2015, leaving a crater estimated to be 16 m in diameter.
The ESA's AIDA mission concept would investigate the effects of impact crashing a spacecraft into an asteroid. The DART spacecraft will impact asteroid 65803 Didymos's moon Dimorphos in 2022, and the Hera spacecraft will arrive in 2027 to investigate the effects of the impact. 
The spacecraft design for Mars Science Laboratory consists of:
|Cruise Stage:||Configuration for travel between Earth & Mars. |
|Entry, Descent, |
and Landing System:
|Configuration for entry into the Martian atmosphere. Includes the aeroshell and a "sky crane" lander structure.|
|Rover:||A wheeled vehicle with science instruments for discoveries on the Martian surface.|
The spacecraft design for the Mars Science Laboratory mission is based largely on the successful twin Viking landers sent to Mars in the 1970s. The rover design is based on the Mars Exploration Rovers, which landed on Mars in early 2004. The system for entry, descent, and landing is entirely new.
The Stardust was a boxy craft that carried two solar arrays, along with a 101-lb. (46 kilograms) sample-return capsule that was dropped into Earth's atmosphere, carrying samples of cometary and interstellar dust. The spaceship carried two dedicated science instruments and several engineering instruments required for spacecraft operation that also collected scientific data:
- The aerogel dust collectors were two tennis-racket-shaped collectors capable of extending from and retracting into the spacecraft. The aerogel covering the collectors kept dust particles pristine as they slowed from high speeds to a dead stop. One side of a collector gathered material from Wild 2 while the other side sampled material encountered as Stardust traveled through space.
- The Cometary and Interstellar Dust Analyzer (CIDA) determined the composition of individual dust grains that collided with a silver impact plate.
- The Navigation Camera targeted the comet, collecting high-resolution images.
- The Dust Flux Monitors monitored the flux and size distribution of particles in Stardust's environment.
The crown jewel of Stardust's instruments was the sample-gathering aerogel. The product is a silicon-based solid with a porous, sponge-like structure and consists mostly of empty space. Because the particles that Stardust aimed to sample were traveling at up to six times the speed of a rifle bullet, a high-speed capture in a conventional collector could alter the particles' shape and chemical composition. But when the high-speed particles hit aerogel, they were captured with minimal heating or chemical alteration.
"Capturing the particles in aerogel was a little bit like collecting BBs by shooting them into Styrofoam," Sanford said.
Each particle created a carrot-shaped track up to 200 times the particle's length in the aerogel, allowing scientists to trace the particles' paths through the mostly transparent material.
Finding primitive extraterrestrial life would be front-page news (or set a record for clicks), but the grand prize is reserved for the “I” in SETI — intelligent life. SETI searches seek signs of technology produced by extraterrestrial intelligence, most likely in the form of “unnatural” radio waves.
In fact, an alien looking for life in the cosmos might very well spot Earth as inhabited by exactly that method. In the 1990s, Carl Sagan and colleagues took advantage of the Galileo spacecraft’s pass by Earth to probe our planet for telltale signals of our existence. The giveaway was narrow-band radio emissions (abundant signaling at a single radio frequency).
“That as far as we know is an unmistakable indicator of technology, and an unmistakable indicator of life,” Siemion said at the AAAS meeting. “And indeed it is the most detectable signature of life on this planet as viewed from a distant vantage point.”
For now, Earth-based radio telescopes listening to the cosmos might hear a deliberate message, but couldn’t pick up TV shows or other radio-wave “leakage” from alien civilizations. But the Next Generation Very Large Array, now in the planning stage, would have the power to receive such unintentional communication, at least from nearby stars.
Perhaps alien civilizations may make more use of lasers than radio, though, which makes the prospect of Laser SETI appealing. But whether patterns are found in the radio or optical region of the electromagnetic spectrum doesn’t matter — such patterns could reveal intelligent activity regardless of their purpose, Siemion pointed out.
“We simply look for compression of electromagnetic energy in time or in frequency or some kind of modulation that is inconsistent with the astrophysical background or the instrumental background and consistent with something that technology could produce,” he said. “So it doesn’t matter if it’s a laser communication system being used to communicate with a spacecraft in some exoplanet system or it’s a giant laser light show that some very advanced civilization produced for the amusement of all the life in their system.”
In any event, receiving a message would be a monumental revelation about the viability of technological civilizations. Nobody knows whether a society that has developed advanced technology can long survive.
“The lifetime of a technological civilization … is a very difficult thing to predict,” said Siemion. “And of course, looking around at our own civilization you have reason to question what that term might be.”
On the other hand, a signal from space would almost certainly be from a civilization that has existed much longer than ours. (Otherwise the likelihood of listening in at exactly the right time would be prohibitively small.) So merely receiving a message might be considered hope that civilization on Earth might not be doomed after all.
Success in receiving a message raises other issues. For one thing, it’s a real possibility that an alien message is clearly an attempt to communicate, but in a language that no earthling could understand. And understood or not, a message received suggests the need to consider a reply. SETI researchers have long agreed that if a signal is detected, no response would be made until a global consensus had been reached on who will speak for Earth and what they would say. But that agreement is totally unenforceable, Tarter pointed out, and nobody has any idea about how to reach a global consensus on anything. (Perhaps the proper reply would just be “HELP!”)
Still, contemplating a response is for the moment a lesser priority than finding a message in the first place. And that might require help from nonhuman intelligence right here on Earth in the form of advanced computers. Recent developments in artificial intelligence research should soon make machine learning an effective tool in the E.T. search, Tarter said at the AAAS meeting.
“The ability to use machine learning to help us find signals in noise I think is really exciting,” she said. “Historically we’ve asked a machine to tell us if a particular pattern in frequency and time could be found. But now we’re on the brink of being able to say to the machine, ‘Are there any patterns in there?’”
So it’s possible that an artificially intelligent computer might be the first earthling to discern a message from an extraterrestrial. But then we would have to wonder, would a smart machine detecting a message bother to tell us? That might depend on whom (or what) the message was from.
“I think there’s something particularly romantic,” said Siemion, “about the idea of machine learning and artificial intelligence looking for extraterrestrial intelligence which itself might be artificially intelligent.”
This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews. Sign up for the newsletter.
NASA Just Landed On An Asteroid - And Hopefully Scooped Up Material For The First Time In Its History
The spacecraft practiced landing on the asteroid earlier this year (pictured).
A NASA spacecraft has successfully landed briefly on an asteroid before taking off again – hopefully grabbing some pieces of the asteroid in the process.
Today at 6.10 P.M. Eastern Time, the van-sized OSIRIS-REx sent a signal that it had reached the surface of the asteroid, touching its surface for just a few seconds. By firing a puff of gas into the surface, scientists are now hoping the arm has scooped material from the asteroid – called Bennu – ready to return to Earth.
"I can't believe we actually pulled this off," Dante Lauretta from the University of Arizona, the lead on the mission, said shortly after the landing. "This is history. It's amazing."
While the landing actually occurred 18 minutes earlier, the spacecraft and asteroid's distance of 334 million kilometers from Earth meant the team had to wait for the signal to arrive to confirm the touchdown was successful.
Now the team will be anxiously waiting for the spacecraft to send back images and to see how much sample the spacecraft managed to grab from the surface of the asteroid. If it's deemed to be enough, they can begin to plan for the journey home.
The team at mission control at NASA's Goddard Space Flight Center celebrated after touchdown was . [+] confirmed.
OSIRIS-REx was launched in 2016, on a mission to the asteroid Bennu – which has a similar orbit to Earth, albeit slightly larger. The goal is to grab samples from the asteroid and return them to Earth, the first asteroid sample return mission in NASA’s history.
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It’s thought asteroids like Bennu could have delivered the building blocks of life to Earth and other worlds. Thus, studying samples from this asteroid back on Earth could have significant implications for our own origins, perhaps helping to explain how life on Earth began.
After the spacecraft reached the asteroid in 2018, the mission’s team began studying its surface, looking for a landing spot. They settled on a relatively flat area called Nightingale, just ten meters across, equivalent to a few parking spaces.
Following a couple of rehearsals, today was set as the date to attempt actually landing on the asteroid. Four and a half hours prior to the landing, the spacecraft was commanded to autonomously descend towards the surface.
An artist's impression of OSIRIS-REx touching the surface.
After about four hours, the spacecraft fired its thrusters in a “checkpoint burn”, 125 meters above the surface, beginning its descent. About 11 minutes later it performed a “checkpoint burn” reducing its speed to a relative velocity of just ten centimeters per second.
Finally, the spacecraft’s extended TAGSAM (Touch-and-Go Sample Acquisition Mechanism) arm contacted the surface, with a spring mechanism bringing the spacecraft to a halt. Nitrogen canisters then fired gas into the surface, hopefully kicking material up into the head of the arm, where it should be captured in its rim.
The spring mechanism then pushed the spacecraft away from the surface before its thrusters fired – dodging a dangerous large nearby boulder called Mount Doom – to take the spacecraft up to a safe distance away from the asteroid.
Here, within a few days, the team will spin the spacecraft with its TAGSAM arm extended. By measuring the inertia of the spacecraft on this spin, they will be able to work out how much sample the spacecraft has collected from the surface.
The team are expecting anywhere from 60 grams up to two kilograms – roughly the weight of a brick. Any less, and they may return to a second planned landing site called Osprey later this year to attempt another sample capture.
OSIRIS-REx drifted over the asteroid before descending to Nightingale.
If the amount of sample is deemed to be enough, however, the spacecraft will leave Bennu in March 2021. It will then make a two-year voyage home, ultimately dropping a capsule containing the samples into our atmosphere in September 2023, which will parachute to a landing in the Utah desert.
For NASA, this mission is a complete first it has never attempted to return material from an asteroid to Earth, although it has returned material from a comet’s tail. It is also the largest sample return mission in history beyond missions to the Moon.
However, it is not the first such asteroid mission. Two Japanese spacecraft have achieved the feat before, Hayabusa1 in 2010, which returned just one millionth of a gram from the asteroid Itokawa, and Hayabusa2, expected to return up to a gram when it returns in December this year.
Now the OSIRIS-REx team face an anxious wait to see how much sample they have scooped up. If it’s enough, they’ll be able to breathe a sigh of relief and prepare for the journey home. If not, they’ll soon need to start planning for another nerve-wracking descent to the surface of Bennu.
‘Big leap for China’
This is China’s first mission to Mars, and makes the country only the third nation — after Russia and the United States — to have landed a spacecraft on the planet. The mission “is a big leap for China because they are doing in a single go what NASA took decades to do”, says Roberto Orosei, a planetary scientist at the Institute of Radioastronomy of Bologna in Italy.
Zhurong now joins several other active Mars missions. NASA’s Perseverance rover, which arrived on 18 February, is several hundred kilometres away from the landing site, and NASA’s Curiosity rover has been poking around the planet since 2012. Several spacecraft are also circling Mars, including the United Arab Emirates’ Hope orbiter, which also arrived in February. “The more the merrier on Mars,” says David Flannery, an astrobiologist at Queensland University of Technology in Brisbane, Australia.
Researchers say that the engineering feat of getting there has taken precedence over science in China’s first tour of Mars, but the mission could still reveal new geological information. They are especially excited about the possibility of detecting permafrost in Utopia Planitia, the region in the northern hemisphere of Mars where Zhurong has landed (see ‘Landing site’).
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An uncrewed Chinese spacecraft successfully landed on the surface of Mars on Saturday, state news agency Xinhua reported, making China the second space-faring nation after the United States to land on the Red Planet.
The Tianwen-1 spacecraft landed on a site on a vast plain known as Utopia Planitia, “leaving a Chinese footprint on Mars for the first time,” Xinhua said.
The craft left its parked orbit at about 1700 GMT on Friday. The landing module separated from the orbiter three hours later and entered the Martian atmosphere, the official China Space News said.
It said the landing process consisted of “nine minutes of terror” as the module decelerates and then slowly descends.
A solar-powered rover, named Zhurong, will now survey the landing site before departing from its platform to conduct inspections.
Named after a mythical Chinese god of fire, Zhurong has six scientific instruments including a high-resolution topography camera.
The rover will study the planet's surface soil and atmosphere. Zhurong will also look for signs of ancient life, including any sub-surface water and ice, using a ground-penetrating radar.
Tianwen-1, or “Questions to Heaven”, after a Chinese poem written two millennia ago, is China's first independent mission to Mars. A probe co-launched with Russia in 2011 failed to leave the Earth's orbit.
The five-tonne spacecraft blasted off from the southern Chinese island of Hainan in July last year, launched by the powerful Long March 5 rocket.
After more than six months in transit, Tianwen-1 reached the Red Planet in February where it had been in orbit since.
If Zhurong is successfully deployed, China would be the first country to orbit, land and release a rover in its maiden mission to Mars.
Tianwen-1 was one of three that reached Mars in February, with US rover Perseverance successfully touching down on Feb 18 in a huge depression called Jezero Crater, more than 2,000km away from Utopia Planitia.
Hope — the third spacecraft that arrived at Mars in February this year — is not designed to make a landing. Launched by the United Arab Emirates, it is currently orbiting above Mars gathering data on its weather and atmosphere.
The first successful landing ever was made by NASA's Viking 1 in July 1976 and then by Viking 2 in September that year. A Mars probe launched by the former Soviet Union landed in December 1971, but communication was lost seconds after landing.
China is pursuing an ambitious space programme. It is testing reusable spacecraft and is also planning to establish manned lunar research station.
In a commentary published on Saturday, Xinhua said China was “not looking to compete for leadership in space” but was committed to “unveiling the secrets of the universe and contributing to humanity's peaceful use of space”.
Chinese spacecraft heading back to Earth with lunar samples
A Chinese spacecraft ferrying rocks drilled from the moon’s surface is on course to land back on Earth Wednesday and deliver the first fresh lunar samples to scientists since the 1970s.
The Chang’e 5 mission’s return spacecraft is in the home stretch of a 23-day mission that successfully launched on China’s most powerful rocket Nov. 23, landed on the moon Dec. 1, collected samples, then took off again Dec. 3 to accomplish the first automated docking between two robotic spacecraft around another planetary body.
Chang’e 5’s ascender vehicle linked up with the mission’s return spacecraft Dec. 5, then transferred the capsule containing the moon rocks to the return craft before jettisoning and intentionally crashing into the moon Dec. 7.
With those steps completed, all that’s left is to bring the lunar samples back to Earth.
Chang’e 5’s return spacecraft fired thrusters to raise its orbit around the moon on Friday, then performed a final departure maneuver at 8:51 p.m. EST Saturday (0151 GMT Sunday) to head for Earth, according to the China National Space Administration. The 22-minute maneuver with four small thrusters provided the impulse necessary for the Chang’e 5 return craft to break free of the moon’s gravity.
The probe completed a course correction burn Monday and continued cruising toward Earth Tuesday, aiming for a landing in China’s Inner Mongolia region Wednesday.
Chinese officials have not disclosed the exact landing time, but public notices directing pilots to steer clear of the mission’s recovery zone are active from 12:32 p.m. until 1:07 p.m. EST (1732-1807 GMT) — in the middle of the night in the remote landing area.
Chang’e 5’s return spacecraft will release the capsule carrying the moon rocks before entering the atmosphere.
The re-entry capsule will bounce off the atmosphere in a “skip re-entry” to slow the craft down before landing, diminishing its initial entry velocity from 25,000 mph, or 40,000 kilometers per hour, significantly faster than a re-entry from low Earth orbit. The skip re-entry will help reduce heat the landing capsule will encounter during descent, Chinese officials said, before the craft deploys a parachute for landing.
Chinese recovery crews in Inner Mongolia are preparing for the arrival of the lunar samples, Chinese state media reported Tuesday.
The Chang’e 5 sample return mission, if successful, will mark the first round-trip flight to the moon in 44 years. It is the first tmie lunar material has been returned to Earth since 1976, when the Soviet Union’s robotic Luna 24 mission brought back around 170 grams, or 6 ounces, of specimens from the lunar surface.
Nine missions have returned moon samples to Earth, including NASA’s six Apollo missions with astronauts, and three robotic Luna spacecraft launched by the Soviet Union. NASA’s Apollo missions brought back 842 pounds (382 kilograms) of rocks from the moon.
Chinese scientists will take the lunar material to a climate-controlled facility to begin analyses on the rocks. Researchers hope to learn about the moon’s history and evolution.
The Chang’e 5 mission’s goal was to collect more than 4 pounds, or 2 kilograms, of rocks for return to Earth. Chinese officials have not released an estimate of how much material the spacecraft gathered on the moon.
The Chang’e lunar program is named for a moon goddess in Chinese folklore.
The sample return mission follows earlier feats in China’s lunar exploration program. Most recently, the Chang’e 4 mission performed the first successful soft landing on the far side of the moon in January 2019. Chang’e 4 uses a dedicated data relay satellite flying in deep space to bounce commands and scientific data between ground teams and the spacecraft on the lunar surface.
China’s next lunar mission, Chang’e 6, is similar to Chang’e 5. It might attempt a sample return mission to retrieve lunar rocks from a location near the moon’s south pole around 2023.
Follow Stephen Clark on Twitter: @StephenClark1.