At the end of every year, news sites publish memorials for all the important people the world has lost. But nobody ever mentions the space robots. Yet in 2013, we had to say goodbye to a lot of great scientific space missions. Far too many space-based telescopes and Earth-observing satellites were either decommissioned, faced unexpected hardware failures, or simply ran out of fuel. That, coupled with the fact that NASA has fairly few future plans for robotic exploration, means a tremendous loss for researchers. Many of these space probes had lived long past their expected lifetimes. All provided spectacular data that have transformed how scientists think about our planet and our universe. Here, we pay a tribute to the amazing robots we said goodbye to in the last year and look at some of the amazing images and data they collected. To start with, there was the European Space Agency’s Herschel space telescope. When looking out at the universe, it’s important to have a variety of eyes. We humans see in a fairly narrow wavelength band of the electromagnetic spectrum. But so many other interesting things are hiding just beyond the frequencies we can see. Launched in 2009, Herschel was able to peer at the cosmos in infrared wavelengths – and was in fact the largest infrared telescope ever put into space. At these frequencies, Herschel could look straight through the gas and dust that typically obscure distant processes. With its infrared eyes, the telescope could watch young stars being born, see organic chemicals form in molecular clouds, and even spot water on Jupiter that was determined to have arrived when comet Shoemaker-Levy 9 crashed into the gas giant in 1994. But in order to see at infrared wavelengths, Herschel required extremely cold liquid helium. That coolant ran out in April as expected, effectively shutting down the spacecraft. Engineers flipped the switch on Herschel, and now it will drift for hundreds of years before coming crashing back and burning up in Earth’s atmosphere. Image: Baby stars in the Rosette nebula, a stellar nursery about 5,000 light-years from Earth. ESA and the PACS, SPIRE & HSC consortia, F. Motte (AIM Saclay,CEA/IRFU - CNRS/INSU - U.ParisDidedrot) for the HOBYS key programme

Planck A mere 380,000 years after the universe was born, it cooled and expanded to the point where photons could travel unimpeded without bumping immediately into another particle. The oldest light in the universe is still with us today, just cooled to an extremely low temperature after traveling for more than 13 billion years. Mapping this cosmic microwave background radiation was the job of the European Space Agency’s Planck spacecraft, which launched in 2009. Planck gave scientists the most detailed look at the cosmic microwave background radiation that they have ever seen. Each photon is almost identical to every other photon in this radiation. But the tiny differences in temperature – each about 0.00001 degrees Kelvin – are extremely important. Each miniscule variation represents a small pocket of density in the early universe that eventually gave rise to the complex structure of galaxies and superclusters we see today. By studying the cosmic background, scientists can better understand how the early cosmos became the place we live in 13.7 billion years later. Planck exhausted its supply of liquid helium in October as expected, and scientists at ESA sent the spacecraft its deactivation command. Image: A view of the tiny variations in the cosmic microwave background. ESA and the Planck Collaboration

Kepler Possibly the thing that most excites people about space exploration is the prospect of finding life on other worlds. But before we can spot ET, we need to know that he has a home. While we’ve speculated about planets around other stars for a long time, it’s only in the last 20 years that we’ve had the technology necessary to definitively find them. NASA’s Kepler space telescope, which was built specifically to find extrasolar planets, is one of the agency’s most celebrated missions. The planet-hunting spacecraft has confirmed the existence of more than 130 weird and wonderful worlds beyond our solar system and has detected thousands of other potential exoplanets. The telescope was launched in 2009 and worked flawlessly for more than four years, lasting beyond its original lifetime plan. But in May, it suffered a critical hardware failure when one of its reaction wheels – gears responsible for ensuring the spacecraft remains perfectly pointed at its target stars – broke. Astronomers mourned Kepler but NASA hasn’t given up on the mission quite yet. Last month, engineers at the agency proposed a new configuration, dubbed K2, which would use pressure from solar photons to balance the spacecraft and keep it staring at the stars. A resurrected Kepler is now being considered for funding in 2014, though it will have to compete for limited money with other favorite telescopes such as Hubble. Image: An artist rendering of an extrasolar planet that orbits two stars at the same time. NASA/JPL-Caltech/R. Hurt

Deep Impact NASA’s Deep Impact mission was actually several missions disguised as one. No other spacecraft on this list flew 7.6 billion kilometers or shot a comet with a projectile. Launched in 2005, the space probe traveled to comet Temple 1 and fired an impactor at the icy body, creating a plume that helped scientists understand the comet’s composition. Follow-up observations with NASA’s Stardust spacecraft confirmed that Deep Impact had formed the first man-made crater on a comet. In 2007, Deep Impact finished its initial mission and morphed into a new one, called EPOXI. Cruising through the solar system, the spacecraft studied extrasolar planets and made a flyby of a second comet, Hartley 2, in 2010. Hartley was approaching the sun at the time and spewing out jets of bright material, which can be seen in EPOXI’s images. Sometime this August, NASA mission control lost contact with the spacecraft and was unable to restore communication. The probe had been taking photos of the famous comet ISON at the time, nearly all of which were lost. Mission scientists suspect that a software glitch caused the communication failure and abandoned further attempts to reach the spacecraft in September. Image: Bright jets of material shoot from comet Hartley 2. NASA/JPL-Caltech/UMD

Landsat 5 Robots often last longer than you expect. For instance, the USGS and NASA’s Landsat 5 satellite initially had a three-year planned mission. It ended up going for nearly three decades. The longest lived Earth-observing satellite in history, Landsat 5 launched in 1984 and diligently watched the world change below it. During its life, it saw cities grow, forests shrink, glaciers retreat, and recorded the first images of key events such as the Chernobyl nuclear accident in 1986 and the devastating 2004 tsunami in southeast Asia. It helped establish a continuous record of our planet that allowed scientists to better understand weather, climate, and humanity’s effect on them. Hobbled by a gyroscope malfunction in 2012, Landsat 5 was officially retired from active duty that year. But it wasn’t until June that the satellite’s operation team transmitted the final command to the spacecraft, terminating the mission. Landsat 5's unexpected longevity saved the mission from a gap in its continuous coverage of Earth when its sibling, Landsat 6, failed to reach orbit in 1993. The probe is survived by two successor spacecraft – Landsat 7 and 8, the latter of which launched in February. Landsat 5 will reenter the atmosphere and disintegrate sometime around 2034. Image: Belcher Islands in Canada. USGS/NASA

GOCE What does our planet’s gravitational field look like? Though the Earth is a sphere, its gravitational field varies in places because of differences in density or mass. A seafloor here, a mountain range there – it all adds up to an uneven field. The European Space Agency’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite started circling the globe in 2009, mapping out the Earth’s gravity in unprecedented detail. The sexy probe used three pairs of accelerometers that measured gravitational gradients as it flew above the planet. GOCE provided information on the boundary between the Earth’s crust and mantle, global ocean circulation patterns, and even detected sound waves produced by earthquakes. Recently, scientists used GOCE data to show that the Earth’s gravitational field was permanently scarred by the enormous 9.0 earthquake that hit Japan in 2011. GOCE ran out of fuel in October and reentered the atmosphere, crashing just south of South America’s tip. Image: Deviations in the Earth's gravitational field, greatly exaggerated in this map from GOCE. ESA/HPF/DLR

JASON-1 Staring at waves all day long is a job for a surfer, or a robot. That’s exactly what the Jason-1 satellite – a joint project between NASA and CNES, the French space agency – did for more than 11 years. Launched in 2001, Jason-1 was part of a series of satellites that created a 20-year record of global ocean circulation. Every 10 days, the spacecraft would map sea level, wind speeds, and wave heights around almost the entire world. The results helped improve global weather forecasts, monitor El Nino/La Nina events, and tracked roughly 4 centimeters of sea level rise since 1992. The probe was joined by a sister satellite in 2008 named Jason-2 and the two often flew in formation taking simultaneous data from opposite sides of the globe. Initially expected to last three years, Jason-1 kept chugging along, even as hardware glitches accumulated. It lost its last remaining transmitter in July and the two space agencies decommissioned the spacecraft. Image: Regional changes in sea level based on the 19-year trend from 1993 through 2012. University of Colorado

GOES-12 It’s strange to think that just 40 years ago, the world didn’t have a set of constant weather-monitoring satellites flying above it. NOAA’s Geostationary Operational Environmental Satellite system, which began operations in 1974, has been a cornerstone of weather forecasts and severe storm tracking. One spacecraft in this system, GOES-12, steadfastly watched the U.S. East Coast for more than 10 years. Launched in 2001, the probe recorded Hurricane Katrina and 2009’s Snowmageddon that crippled the eastern seaboard, among other important events. In 2010, the GOES-12 was shifted to a new position above South America where it provided information on volcanic ash clouds, wildfires, and drought. In August, the spacecraft was decommissioned. Its remaining fuel was used to park it in a higher orbit, its battery was disabled, and the machine’s transmitters were turned off. It is survived by GOES-13 and GOES-15, which watch the East and West Coasts, respectively. Image: Hurricane Katrina, shortly before it made landfall in Louisiana. NOAA