When it comes to science, exploring the future and digging into the past are equally crucial to enable the human race to learn, survive and thrive. Here, 2015 will be remembered for two path-breaking discoveries - the presence of water on Mars and discovery of a brand new human relative.
In its constant search of alien life in space, NASA's Mars Reconnaissance Orbiter (MRO) in September obtained the first definitive signs of liquid water (briny) flowing intermittently on the surface of the Red Planet.
In a paper published in the journal Nature Geoscience, the team led by Lujendra Ojha, a researcher of Nepalese origin from the Georgia Institute of Technology (Georgia Tech) in Atlanta, looked at streaks that form on some slopes on Mars during warmer times of the year, having previously suspected they might be caused by flowing, salty water.
The discovery hints towards a full-fledged life that may have sustained on the Red Planet in the past.
"There is liquid water today on the surface of Mars," Michael Meyer, lead scientist of NASA's Mars exploration programme, said in a statement.
In December, Curiosity found mysterious rocks rich in silica - a rock-forming chemical combining the elements silicon and oxygen and commonly seen on Earth as quartz - bolstering the presence of water on the Martian surface.
In September, the world woke up to welcome a new member of the human species that globally made the home pages of all top publications.
Homo naledi - a broad-chested fellow who walked upright and had a face with a smile that was probably more human than ape-like years ago - was uniquely adapted for both tree climbing and walking as dominant forms of movement, while also being capable of precise manual manipulation.
Lead author William Harcourt-Smith from University of the Witwatersrand in South Africa describes H naledi's foot based on 107 foot elements from the Denaldi Chamber, including a well preserved adult right foot.
"H naledi foot shares many features with a modern human foot, indicating it is well-adapted for standing and walking on two feet. However, it differs in having more curved toe bones," Harcourt-Smith noted in a paper published in the journal Nature Communications.
In the middle of the year, two big events grabbed the eyeballs. First, NASA's New Horizons probe -- after travelling over 4.8 billion km -- flew past the mysterious Pluto dwarf planet on July 14. Since then, the mission has been beaming a Pluto "treasure trove" to Earth.
In what may necessitate rewriting of science books, the probe has returned the sharpest images ever of cratered, mountainous and glacial terrain on Pluto and the best close-ups of the mysterious system that humans have seen for decades.
After its historic July 14 flyby of the Pluto system, NASA has selected the next potential destination for its New Horizons mission - a small Kuiper Belt object (KBO) known as 2014 MU69 that orbits nearly a billion miles beyond Pluto.
Later in July, NASA's Kepler mission confirmed the first near-Earth-size planet in the "habitable zone" around a Sun-like star.
The newly discovered Kepler-452b is the smallest planet to date discovered orbiting in the habitable zone - the area around a star where liquid water could pool on the surface of an orbiting planet -- of a G2-type star, like our Sun.
"We can think of Kepler-452b as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth's evolving environment," said Jon Jenkins, Kepler data analysis leader at NASA's Ames Research Center in Moffett Field, California.
The International Space Station (ISS), with humans on board, turned 15 in November, enabling research breakthroughs and driving technology innovations that will provide benefits on the Earth and enable long-duration human and robotic exploration missions into deep space, including Mars.
After having a sumptuous feast of "Outredgeous" red romaine lettuce grown in space in August, ISS astronauts were set to witness flowers blooming on the orbiting laboratory after the New Year.
"Growing a flowering crop is more challenging than growing a vegetative crop such as lettuce," said Gioia Massa, a NASA Kennedy Space Center payload scientist.
In December, with the opening of hatches between the ISS and an arriving Soyuz spacecraft, three new Expedition 46 astronauts joined the three ISS residents to continue key research that advances NASA's journey to Mars while making discoveries that can benefit humanity.
* After 10 years, NASA's New Horizons probe flew past the mysterious dwarf planet Pluto on July 14.
* NASA's Kepler mission confirmed the first near-Earth-size planet in the "habitable zone" around a Sun-like star in July.
* The Mars Reconnaissance Orbiter (MRO) in September obtained first-ever definitive signs of liquid water flowing intermittently on the surface of present-day Mars.
* In September, scientists unearthed a new member of the human species called Homo naledi who walked upright and had a face with a smile that was probably more human than ape-like years ago.
* The International Space Station (ISS) with humans on board turned 15 in November,
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