In six decades of missions to Venus, much has been learnt about the “hellish” hot, cloudy and acidic conditions on the second planet from the Sun.
But many questions remain, including why Venus developed such an extreme climate, whether volcanic activity continues and if cooler parts of the atmosphere contain micro organisms.
A mission announced this week by the UAE could help scientists gain a better understanding of a planet very similar in size and density to Earth, but very different in character.
Sheikh Mohammed bin Rashid, Vice President and Ruler of Dubai, unveiled plans for a mission to launch in 2028 that will visit Venus and explore seven asteroids in the Asteroid Belt, a circular region of the solar system that approximately fits between Mars and Jupiter.
“I’m sure this will be helpful in the overall context of Venus science. It is likely to be one of several missions to Venus in the next decade,” said Ian Crawford, professor of planetary science and astrobiology at Birkbeck University of London.
Nasa, previously accused of neglecting the planet, recently announced two Venus missions, expected in 2028 to 2030, to analyse its atmosphere, geological features and surface topography.
The European Space Agency’s EnVision Venus orbiter is expected to launch in the early 2030s, collecting data that could help scientists understand why Earth and Venus are so different.
The early missions to Venus
Missions to Venus began in the early 1960s, with the former Soviet Union and Nasa launching numerous spacecraft, although much of this early exploration was unsuccessful.
Several fly-bys were achieved, however, and spacecraft also entered Venus’s atmosphere, with the 1967 mission by the Soviet Union’s Venera 4 indicating that this atmosphere was rich in carbon dioxide. The planet is also covered in thick sulphuric acid clouds.
Venus’s atmospheric pressure is 92 times that of Earth at sea level – enough, it has been said, to crush submarines – and it traps energy from the Sun and from Venus itself, creating a surface temperature of about 467°C, highly inhospitable for life, including astronauts.
“Manned missions are all but impossible,” Prof Crawford said. “There have been a handful of robotic missions, all Russian spacecraft, from the 1970s, which successfully parachuted and landed.”
It is, he added, “virtually impossible for equipment to survive very long” on the planet, given the extreme conditions.
Venera 7, another Soviet mission, landed on Venus in 1970, although its parachute ripped on the way down and the spacecraft transmitted only weak signals back to the Earth.
Venera 8 landed on Venus in 1972, achieving what has been described as the first completely successful landing on another planet.
Three years later Venera 9 took pictures on the surface, while in 1978 a Nasa spacecraft, Pioneer, provided evidence that there may once have been oceans on Venus.
A 1989 Nasa orbiter, Magellan, used radar to determine that the surface of Venus was highly volcanic.
“It carried a radar that penetrated through the clouds,” said Prof Crawford, explaining that it indicated that the surface was also relatively young, perhaps formed from volcanic activity 500 million years ago.
“This seems very old, but in the history of the solar system, that’s quite recent.”
There have now been about 40 missions to Venus, a planet that typically takes spacecraft about four months to reach – abaout 40 times as long as it takes to get to the Moon.
A planet still poorly understood
Despite these many missions, Prof Jane Greaves of the School of Physics and Astronomy at Cardiff University in the UK said Venus remained poorly understood because “most telescope observations see only the cloud tops”.
Prof Greaves and a team of other astronomers announced a year ago that by using powerful telescopes they had detected signs of a rare molecule called phosphine, made of hydrogen and phosphorus, in Venus’s clouds.
On Earth, phosphine is made by micro organisms in environments without oxygen, so the discovery raised the intriguing prospect that there may be life in Venus’s upper atmosphere.
Further missions by spacecraft to Venus could lead to a better understanding of Venus’s atmosphere and indicate whether life really may exist there.
“Follow-up could include confirming [the presence of phosphine] by direct sampling in the clouds, and looking for other molecules like ammonia or methane that could be life-related,” Prof Greaves said.
Research has indicated that for billions of years Venus’s surface had moderate temperatures and liquid water, tying in with Nasa’s observations that there may have been oceans, and even living organisms.
But conditions changed about 700 million years ago and since then the surface of Venus has been extremely hot. Researchers are keen to discover more about what caused this shift.
Asteroids and what formed the Solar System
The main Asteroid Belt, which the newly announced UAE mission will also visit, is home to asteroids that originate from the collision and fragmentation of larger objects about 4.6 billion years ago, when the solar system formed.
It contains 1.1 million to 1.9 million asteroids larger than one kilometre in diameter, according to Nasa, plus millions of smaller asteroids, and is where most meteorites that strike Earth originate.
Among the pioneering missions to understand asteroids was Nasa’s Galileo, which in 1991 achieved the first fly-past of an asteroid. It was another decade before the first landing on an asteroid, when Nasa’s Near spacecraft touched down on Eros.
There have since been numerous other asteroid missions, including one by Japan’s Hayabusa, which returned asteroid dust to Earth in 2010, five years after it landed on the asteroid Itokawa.
In December 2020, six years after launching, another Japanese spacecraft, Hayabusa 2, brought back samples from the asteroid Ryugu.
Just as several Venus missions are planned, there is much to look forward to when it comes to asteroid science.
Forthcoming missions include that of Nasa’s Lucy, scheduled to launch from Cape Canaveral in Florida on October 16 on its way to visit one Main Belt asteroid in 2025 and seven Trojan asteroids between 2027 and 2033.
Through cameras and other instruments, Lucy should give researchers details about the surfaces and properties of the asteroids, offering clues about the solar system’s formation.