The two newborn exoplanets, as orbs outside our solar system are called, are estimated to be less than 10 million years old and orbit embryonic stars hundreds of billions of kilometres away.

One of the planets, the fully formed K2-33b, is about 50 per cent larger than Neptune. Every 5.4 days, it makes a complete circuit around its youthful parent star.

The other exoplanet is a giant Jupiter-like orb circling a star that is probably only 2 million years old - a true babe, in solar terms. But it's 100 times closer to its star than our gas giant is to the sun.

The two independent studies, published in the journal Nature, provide direct evidence that large planets can venture much closer to their host stars than scientists thought possible.

K2-33b could have started in a farther-out orbit before quickly migrating inward. Alternatively, it could have formed in place.

"These are astounding snapshots of planets under 10 million years old," said Swinburne University astrophysicist Alan Duffy. "If this was a family album, these would be pictures of newborns!"

Initially spotted by the Kepler Space Telescope, K2-33b first showed its enigmatic face as a periodic dimming in the light emitted by its host star.

Using both of their 10-metre telescopes, scientists at Hawaii's Keck Observatory, a joint venture between the California Institute of Technology, the University of California and NASA, confirmed that the detected object was indeed a planet.

"We measured the radial velocity of the star over time and confirmed that its orbiting companion was a planet," said Trevor David, first author on the K2-33b paper.

"Our data also confirmed the youth of the star, as well as enabling us to measure its temperature and how fast it rotates – while ruling out the presence of additional stars in the system."

Trying to determine the properties of these planets is difficult. For one thing, the young stars are violent and changeable and can mask the subtle signs that a planet's gravity is pulling on the star.

Scientists dismiss the chance of life, even as we don't know it, existing on these worlds. "In order for a planet to host life as we know it, the basic prerequisite condition is considered to be liquid water," said Keck operations manager Randy Campbell.

The range of orbital distances for a planet to have liquid water is termed the habitable zone. "The planets discovered in this new study are too close to their host star to be in this zone and are likely much too hot for liquid water to exist," Dr Campbell explained.

Even if conditions were potentially hospitable, these worlds are so young that life would not have had a chance to form.

"We don't know how long life takes to arise," Dr Duffy said. "Our only example is Earth, where, it seems, life took hundreds of millions of years to get going. So, a few million years seems far too quick."

So far, exoplanet searches have revealed many massive worlds, known as hot Jupiters because they are close to their host stars. But all of these were much more mature stars.

Two decades ago, scientists knew of only one star with planets – our sun. Today, more than 3200 such systems have been catalogued, ranging from giant planets larger than Jupiter but hotter than Mercury to frozen worlds orbiting moribund stars.

Advances in telescope technology should enable scientists to discern the atmospheric make-up of at least some of these remote and mysterious realms in future.

Surface water is unlikely to exist in liquid form on most of the worlds found so far. But, scientists say, it is only a matter of time before more Earth-like exoplanets, which might be favourable to life, are observed.

The nearest habitable orb may be little more than a few light years away, some research suggests. This will be tested by a new NASA satellite, called TESS, which stands for Transiting Exoplanet Survey Satellite. It's expected to launch next year and will find habitable Earth-like exoplanets near us across the entire sky.

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