2015 is going to be a hard year to top in spaceflight and astronomy.

We continue to learn more about Mars from a pair of rovers and four orbiters. The Curiosity rover passed sol (Martian day) 1210 of its 669 sol primary mission. The car-sized rover recently reached “Namib Dune,” a rippling sand dune near the base of the mountain in the middle of Gale Crater. Curiosity was sent a list of tasks, including measuring the dust in the atmosphere, some additional imaging for a 360-degree panorama of that dune, and some X-ray analysis of rock material.

On the opposite side of the planet, the Opportunity rover has been studying the southern side of Marathon Valley through the fall. This north-facing slope allows the golf-cart-sized rover to maximize sunlight on its solar panels as days grow shorter on Mars. Daylight will slowly increase following Mars’ winter solstice on Jan. 3, 2016.

Observations from NASA's Mars Reconnaissance Orbiter (MRO) also provided the strongest evidence yet that liquid water flows intermittently on present-day Mars. Dark streaks appearing on slopes during warmer months provided clues to the presence of brine under the surface in a liquid state. Hydrated salts lower the freezing point of water sufficiently for liquid water to flow down the slope.

It was a pretty good year on the launch pad. China brought the overall record to 82-3-2 earlier this week with the launch of a geosynchronous satellite. Those two partial failures included a Russian ISS cargo resupply mission that lost attitude control after a successful launch. Two months later, SpaceX had its first launch failure when a failed strut ruptured a second-stage helium tank, disintegrating the Falcon 9 rocket and its ISS resupply payload. SpaceX successfully returned to flight six months later (more on that later).

The Japanese Space Agency (JAXA) saved its Venus Climate Orbiter mission in 2015. After the original orbital insertion plan failed in 2010, JAXA engineers placed the spacecraft in safe mode to conserve resources and began work on a plan to use smaller maneuvering engines to put the craft into orbit around Venus. We can look forward to learning more, though more slowly due to a more highly elliptical orbit than planned, about clouds and stratification within the atmosphere of Venus.

The mission that received the most attention in 2015 was New Horizons. The baby grand piano sized spacecraft returned spectacular images of Pluto and will continue to return more images and data into 2016.

Scientists were most surprised by Pluto’s complex, relatively young surface. The freshly resurfaced nitrogen-ice sheet were described as “one of the youngest surfaces we’ve ever seen in the solar system,” by Jeff Moore of New Horizons’ Geology, Geophysics and Imaging team. Primary Investigator Alan Stern also commented on the many tall mountains on Pluto but was most surprised that no new moons were discovered during the fly-by.

We’ve known Pluto had a feeble atmosphere since observations in 1988 revealed it. But what we didn’t expect was that it extends out 93 miles above the surface. The blue sunrise observed in Pluto’s extremely thin atmosphere as it passed between the spacecraft’s cameras and sun also surprised scientists.

Geology and atmospheric science aside, the heart-shaped region extending across Pluto’s southern hemisphere, informally named Tombaugh Regio to honor of Pluto's discoverer, Clyde Tombaugh, really connected with people who don’t normally pay much attention to planetary exploration.

The 2015 event in space exploration that may prove to be the most memorable happened just a few days ago. SpaceX returned to flight with a launch of a cluster of communications satellites aboard their improved Falcon 9 rocket from the Kennedy Space Center. This successful upright landing of the rocket’s first stage on the company’s new landing facility 5 miles south of the launch pad has the potential to change spaceflight.

Today, it costs $10,000 to put a pound of payload in Earth orbit. Much of that is in from expendable vehicles, especially the core booster where much of the power needed to escape Earth’s gravity well comes from. Reusing that booster can significantly bring down the cost of getting to space.

The 14-story booster that returned to Earth on Dec. 22 was moved to a newly constructed hanger at NASA’s historic Launch Complex 39, where all Space Shuttle and Apollo era missions were launched. The company plans to test fire the booster on launch pad 39B after technicians complete their inspections.

Check back tomorrow for a look ahead at what to look for in 2016 in space exploration and astronomy.

Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.