It is a season of remarkable milestones for space explorers. This month, the New Horizons probe hurtled past Pluto at 45,000kmh, taking rapid snapshots, which Nasa then posted on Instagram.
The photos finally complete our solar system's family portrait, 25 years after the last new snap of a heavenly body, when the Voyager 2 space probe flew by Neptune and gave us a close-up look at the planet for the first time.
But the first photographs of a planet in deep space were of the blood-red fourth planet Mars, and were taken by the Nasa space probe Mariner 4, on July 14 and July 15, 1965. The photographs came amid a race between the United States and the USSR - then locked in a Cold War - to prove their superiority in space. It kicked off a space odyssey that involved not only the Apollo 11 manned mission to the moon in 1969 but the design and construction of an array of spacecraft that were cheaper and could explore more distant worlds.
The total cost of the Mariner 4 project was US$83.2 million, while New Horizons cost approximately US$700 million (S$960 million). The photographs they sent back, however, are considered priceless.
Among the initial pictures beamed back by New Horizons was one of a near-perfect heart shape on the surface of Pluto. And from the treasure trove of information revealed by the fly-by, we learnt that Pluto has mountains rising 3.3km above the surface, and these are likely standing on a bedrock of water ice.
"It's just amazing. It's truly a hallmark in human history," said Nasa's science mission directorate head John Grunsfeld, after the encounter with Pluto. "It's been an incredible voyage," he said, adding that the images showed Pluto to be an "extraordinarily interesting and complex world".
Adding to the celebration, the National Aeronautics and Space Administration released a new image of the "Blue Marble" last week - it was Earth's latest selfie and the first since 1972. The original Blue Marble picture, taken by the crew of Apollo 17, is thought to be the most reproduced photo of all time.
But the new image, taken on July 6 with the Earth Polychromatic Imaging Camera (Epic) aboard the Deep Space Climate Observatory (DSCOVR), looks a little bluer because the photo was not colour-corrected to account for sunlight scattered by air molecules. This gives the DSCOVR photo a distinct hue.
It was taken at a distance of 1.6 million km, while the original shot was taken at a distance of 45,000 km. "The high quality of the Epic images exceeded all our expectations in resolution," said DSCOVR project scientist Adam Szabo.
"The images clearly show desert sand structures, river systems and complex cloud patterns. There will be a huge wealth of new data for scientists to explore," he added.
More exciting news was to come later in the week, with the discovery of "Earth 2.0", a planet 1,400 light years away from our Earth in the constellation Cygnus.
The planet, Kepler-452b, is about 60 per cent bigger than Earth and is located in the habitable zone of its star, where life-sustaining liquid water is possible on the surface. Researchers have speculated that its gravity could be twice that of Earth and that it is most likely rocky.
Scientists using the Kepler space telescope have also confirmed the existence of another 11 planets that could sustain life - from among 521 possible new planets revolving around stars like our own Sun. "Today, Earth is a little less lonely," Kepler researcher Jon Jenkins said.
But mankind's exploration of the universe is not over, it appears. New Horizons has left Pluto behind and is well on its way into the Kuiper Belt, where other dwarf planets, asteroids and frozen bodies composed of methane, ammonia and water will be studied.
Planetary scientist Alan Stern, who is the New Horizons principal investigator, said the spacecraft "could go on for another 20 years".
Meanwhile, having completed their original missions, the storied Voyager 2 space probe and its twin, Voyager 1, are now on an "interstellar mission" in outer space to find out what's beyond our solar system.
Another search continues to find the answer to the question at the heart of space exploration: Are we alone in the universe?
To advance the search for extraterrestrial intelligence, a five-year project has been launched under the aegis of the Breakthrough Prize Foundation, with US$100 million in funding from a Russian billionaire, and the backing of renowned astrophysicist Stephen Hawking, to scan the universe for life.
The project will use Australia's Parkes radio telescope, one of the largest in the world, to look for signals that could be transmitted by advanced civilisations.
"The difficulty is to know what sort of signal we are looking for," said the lead scientist working on the project, Professor Matthew Bailes from Swinburne University in Melbourne. "There is no manual on how to find aliens. We'll have to imagine the sort of transmissions an alien race might send," he added.
"It will be the equivalent of tuning into 400 HDTV channels at once. We'll look for signals of signs of life within those channels," he said.
The solar system: A family album
The smallest planet in our solar system, Mercury is only slightly larger than the Earth's Moon. Its dayside is super-heated by the Sun but, at night, temperatures drop hundreds of degrees below freezing. As the iron core of the planet cooled and contracted, the surface of the planet developed wrinkles that can be up to 1.6km high and hundreds of kilometres long.
Venus' thick, toxic atmosphere traps heat in an excessive "greenhouse effect", with temperatures hot enough to melt lead. It spins slowly in the opposite direction to most planets - the Sun rises in the west, sets in the east. The pressure felt by a human on the surface would be equivalent to that deep beneath the sea on Earth.
Jupiter is a gas-giant planet and therefore does not have a solid surface, though it is predicted that it has an inner, solid core about the size of Earth. Its atmosphere is mostly hydrogen and helium. The planet's swirling cloud stripes are punctuated by massive storms such as the Great Red Spot, which has raged for hundreds of years.
Saturn's rings are made mostly of chunks of ice and small amounts of carbonaceous dust. The rings stretch out more than 120,700km from the planet, but are only about 20m thick. Like the other gas giants, Saturn is mostly a massive ball of hydrogen and helium.
Uranus' equator is nearly at right angles to its orbit, possibly due to a collision with an Earth-sized object. Uranus has more methane in its atmosphere than Jupiter or Saturn. Most of the planet's mass is made up of a hot dense fluid of "icy" materials - water, methane and ammonia.
More than 30 times as far from the Sun as Earth, the planet takes almost 165 Earth years to orbit our Sun. Large storms whirl through its upper atmosphere, and high-speed winds track around the planet at up to 600m per second. Discovered in 1846, it has 13 confirmed moons.
A person on Pluto would weigh 1/15 of what he weighs on Earth. Pluto is unlikely to have a magnetic field due to its small size, low density and slow rotation. It has a very large moon that is almost half its size named Charon, which was discovered in 1978.
It is half the diameter of Earth, but has the same amount of dry land. Surface gravity is only 37 per cent of the Earth's, so you could leap nearly three times higher on Mars. It has the tallest mountain in the solar system, Olympus Mons, a volcano that is 21km high and 600km in diameter.