To boldly go where no man has gone before

The Milky Way

Not quite as many people as stars in our galaxy attended NASA astrophysicist Dr Natalie Batalha’s mind-blowing lecture A Planet for Goldilocks: The Search for Evidence of Life Beyond Earth this week, but the audience nearly filled the War Memorial Theatre. Among those to join Dr Batalha on her journey into a neighbourhood in our galaxy was reporter Mark Peters.

On October 9, the 248th anniversary of the day Lieutenant James Cook shared a kiss by the Turanganui River with a Rongowhakaata man, NASA astrophysicist Natalie Batalha made her Gisborne presentation of A Planet for Goldilocks: The Search for Evidence of Life Beyond Earth.

Lieutenant Cook’s 1769 bon mot, “Ambition leads me not only farther than any other man has been before me, but as far as I think it possible for man to go” holds just as true for NASA’s Kepler Mission outlined by Dr Batalha.

Launched in 2009, the aim of the mission is to find planets that orbit other stars like our Sun. These are known as exoplanets — planets that revolve around stars other than the Sun. Hold your hand up to the Milky Way. The patch it covers is the size of the area explored by the Kepler Space Telescope.

The space telescope has discovered more than 4000 previously unidentified planets that orbit stars. About fifty of those planets have liquid water.

“We look for planets where liquid water would pool on the surface. Not too cold or too hot,” said Dr Batalha. “These are potential cradles of life.”

Three pathways lead to identifying life beyond Earth. Geysers exist on Enceladus, Saturn’s sixth largest moon. Water vapour and ice particles burst out of hydrothermal vents from an underground ocean beneath the moon’s icy crust. In this plume of material are organic compounds, volatile gases, carbon dioxide, carbon monoxide, salts and silica.

“Maybe there’s life in small niches down there. We know Mars had water once. There might be running water deep down in caves or just beneath the surface. But if there is no life, there might be death.”

Future missions, manned or unmanned, could visit the planet and dig up fossils. Radium dishes offer another pathway. They scan the skies for signals that cannot be detected by telescopes. No significant signal has been found — yet.

Because faraway planets are often too faint to be observed, and can be swamped by the glare of a sun-like star, the Doppler wobble presented astronomers with a third way of identifying exoplanets.

“Planets orbit stars but stars also orbit planets. With the influence of the planet’s gravitational tug, the star wobbles.”

That is, the extrasolar planet can be detected from the way its gravity pulls the star slightly back and forth. Minute changes in the star’s regular pulses of radiation are revealed not directly through a telescope but in a spectrograph.

“We take a rainbow of colour and spread it out. Black bands in the spectrum are absorption lines. This is the Doppler shift.”

That wobble provides astrophysicists with information about the planet. The Doppler wobble enabled the first discovery of an exoplanet orbiting another star in 1995. The Jupiter-size planet, 51 Peg, circles what Discover magazine describes as “a fairly mediocre star” 57 light-years away in the constellation Pegasus.

One method used by NASA scientists to find a true Sun-Earth analogue was that used by Cook four months before he arrived at Turanganui a Kiwa. In June, 1769, a pan-European collaboration took the explorer on a scientific expedition to Tahiti. His mission was to observe Venus transit across the face of the sun. This would help scientists identify an astronomical unit with which they could measure the solar system. The Kepler space telescope looks for exoplanets by watching stars dim as their planets transit in front of them.

“We use the idea Cook used in the 1700s. We can measure brightness. When a planet transits across the sun the light dips.”

Kepler is fitted with a mirror, a photometer, that monitors the brightness of more than 145,000 stars. The data is transmitted to Earth, then analysed to detect periodic dimming caused by exoplanets that cross in front of their host star. Periodic dips in light indicate the presence of an exoplanet. The transit method shows how much the starlight dims. From this information, scientists can calculate the size of the planet.

In 2015, the Kepler mission confirmed the first near-Earth-size planet in the “habitable zone” around a sun very similar to our star. Kepler-452b, sometimes referred to by NASA as Coruscant, is an exoplanet that orbits the Sun-like star Kepler-452 about 1400 light-years from Earth in the constellation Cygnus. It is the first potentially rocky super-Earth planet discovered orbiting within the habitable zone of a star very similar to the Sun. Kepler-452b is 1.6 times the size of Earth and has a calendar year of 385 days.

“I’ve learned the planets out there in the Milky Way are more diverse than planets in our solar system,” said Dr Batalha. “We have found the most weird planets out there.”

Among them are planets that orbit dead stars; planets so blasted with radiation from parent planets they have oceans of molten rock, and a system of planets that orbit two stars. Then there are planets that are as old as the universe itself.

The capacity for advanced information collection will advance with developing technologies. Several developments are on the drawing board. NASA’s Transiting Exoplanet Survey Satellite (TESS) mission has been cleared to advance into the development phase. The aim of the TESS mission is to search the entire sky for planets outside our solar system.

Scheduled to launch next year or in 2019, the James Webb Space Telescope is part of NASA’s Next Generation Space Telescope programme. With its 6.5 metre aperture, the JWST is designed to observe some of the most distant events and objects in the universe, such as the formation of the first galaxies.

There are two philosophical camps around the question of exoplanets that might be home to life-forms, said Dr Batalha. Given the plurality of worlds that are potential cradles of life, how can there not be life out there, is one argument. The other is that an astonishing number of coincidences occurred for life to evolve on Earth. This implies life as we know it is unique to this planet. Whatever the answer, human kind is at the mercy of its biology.

“There is something in our DNA that demands we be explorers,” said Dr Batalha. “For the first time in history we have been able to embrace systematic scientific pursuit of an answer to the question ‘is there life in other worlds?’