This story was updated at 6:15 pm ET.
A new Japanese space probe is poised to launch toward Venus to help solve the enduring mysteries of the hellish, cloud-covered world, which has been often described as Earth's twin. But the ambitious spacecraft will have to wait for better weather on Earth.
The Venus Climate Orbiter Akatsuki, which means "Dawn" in Japanese, was slated to launch from Tanegashima Space Center in Japan today on a 2-year mission to study the weather and surface of Venus in unprecedented detail. But low clouds and foul weather prevented its planned liftoff at 5:44 p.m. EDT today, though it was early Tuesday morning local time at the launch site. A new launch target was not immediately available.
"Once we can explain the structure of Venus, we will be able to better understand Earth," said Akatsuki project scientist Takeshi Imamura in a statement released by the Japan Aerospace Exploration Agency (JAXA). "For example, we may discover the reasons that only Earth has been able to sustain oceans, and why only Earth is abundant in life."
Imamura has called Akatsuki "the world's first interplanetary probe that deserves to be called a meteorological satellite."
The probe carries five different cameras to study Venus' clouds as well as map the planet's weather and peer through its thick atmosphere to view the surface. It will join Europe's Venus Express already in orbit around the planet, and has scientists on that mission eager as well.
"Venus somehow transformed from a more Earth-like place to the alien place it is today, and what's fascinating about the world is figuring out how it diverges from the Earth and the history behind why that happened," said David Grinspoon, curator of astrobiology at the Denver Museum of Nature and Science and an interdisciplinary scientist on the Venus Express mission. "It could help us understand how things here might change."
Akatsuki will launch atop a Japanese H-2A rocket and won't be alone during blastoff. JAXA is launching several smaller satellite experiments with the mission, including an ambitious solar sail designed to tag along on the trip to Venus. [More on Japan's solar sail mission.]
Secret of Venus' super-rotation
One of Akatsuki's main goals is to understand what may be the biggest mystery of Venus the "super-rotation" of its atmosphere, where violent winds drive storms and clouds around that planet at speeds of more than 220 mph (360 kph), some 60 times faster than the planet itself rotates.
"There's no consistent model of Venus's climate that can reproduce this super-rotation," Grinspoon explained. "We've been taking general circulation models from Earth and tweaking them for Venus, and they don't work. By understanding better how climate works on Venus, it will make us better understand how climate change on Earth works."
Akatsuki will monitor Venus in the infrared to learn more about the atmosphere and surface under the murky clouds, hopefully revealing what mechanism is driving this super-rotation.
But Imamura has said his team is fully prepared to be surprised by unexpected findings which may uncover more questions than answers.
"We may be pleasantly surprised by the emergence of a greater mystery than super-rotation," he said.
The Venus Express spacecraft the European Space Agency launched in 2005 intriguingly found evidence of lightning on the planet, even though none should exist.
"What creates lightning on Earth is water droplets and ice crystals in clouds, which leads to the separation of electric charges that lightning needs, and you don't have that kind of weather on Venus," Grinspoon said.
But Venus is covered with thick clouds of sulfuric acid.
"Maybe there's a kind of weather we haven't seen yet on Venus that causes this lightning, or maybe how we're wrong about the kinds of conditions needed to make lightning," he added.
Akatsuki should help capture vital clues about this lightning with a camera dedicated to photographing it.
Weird stripes on Venus
There are unusual stripes in the upper clouds of Venus dubbed "blue absorbers" because they strongly absorb light in the blue and ultraviolet wavelengths. These are soaking up a huge amount of energy nearly half of the total solar energy the planet absorbs. As such, they seem to play a major role in keeping Venus as hellish as it is, with surface temperatures of more than 860 degrees F (460 degrees C).
"We don't know what they are," Grinspoon said. "They're probably some kind of sulfur compound, but we haven't been able to nail it down yet."
Akatsuki's ultraviolet imager will focus on inspecting these enigmas.
A bright mystery, and volcanoes?
In 2007, two-thirds of the Venus?s southern hemisphere was suddenly covered in a bright haze that disappeared a few days later. It remains uncertain what started this amazing transformation.
"We think it's some kind of dynamic overturning of the atmosphere that injected sulfur dioxide above the clouds briefly, but we're not sure," Grinspoon said.
The clouds may be fueled from sulfur spewed up by volcanoes on Venus, as Grinspoon and his colleagues ran calculations that suggest the sulfur seen in the atmosphere should dissipate after 10 to 30 million years if not otherwise refueled. However, Venus's clouds are so thick that no one has actually seen any volcanoes yet.
"Venus guards her secrets rather tightly, and under forbidding conditions," he said. The scientists behind Akatsuki hope its cameras might be able to spot active volcanoes under her veil.
When Akatsuki reaches Venus in December, it will find Venus Express there as a partner in orbit, complementing it in a number of ways.
For instance, they will take different orbits over the planet while Venus Express has an orbit that takes it over both poles, enabling it to see virtually the entire world, Akatsuki will fly an elliptical orbit around the equator, allowing it to concentrate on parts of the atmosphere for hours at a time. The orbit will bring Akatsuki as close as 186 miles (300 km) to Venus and as far away as 49,709 miles (80,000 km).
"Venus Express and Akatsuki are like sister satellites, and a very good cooperative relationship has been built as we have progressed in our missions," Imamura said.
Imamura said that while Venus Express primarily studies the chemical composition of Venus' atmosphere, Akatsuki will focus on the fluid motion of the planet's weather. Together, the two spacecraft should reveal a comprehensive picture of how the planet works.
"If there's one thing we've been learning about Venus, it's that it's a really dynamic planet that's very changeable, so we need as much long-term data as we can to build up an understanding of how things change over time," Grinspoon said. "Having Akatsuki there should help capture more vital clues to understanding Venus's mysteries."
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