"So the existence of a planet similar to Earth somewhere, is, in my mind a certainty," she told CNN Light Years.
"Less certain is if such a planet is near enough to us that we can find and identify it sometime in the future," she said.
When as how soon can we find another Earth, she said it depends on how we identify Earth.
If we want a true Earth twin, that is a planet with a thin nitrogen atmosphere, a planet with oceans and continents and orbiting a sun-like star, it will be well over a decade before we have the sophisticated space telescope tools to find and identify one, she said.
"Our best bet is to expand our definition of Earth to big Earths orbiting small stars. We can use the future James Webb Space Telescope to search for signs (of) habitability and signs of life in the planet atmosphere.
"If we would be satisfied to just find an Earth-size or Earth-mass planet, that has already been done.
"But I caution that Venus and Earth appear the same size and mass, yet Venus is inhospitable to life due to a massive greenhouse atmosphere that creates surface temperatures hot enough to melt lead, while Earth has a surface oasis in comparison," she added.