1.Scientists believe there is a possibility that aliens are listening to us on Earth.
there is a possibility that 可能
I accept that there is a possibility that the negative events that I imagine can happen.
我安然接受,想象中会发生的糟糕事件确有发生的可能性 。
2.The scientists said it was highly unlikely that Oumuamua was a sign that aliens exist.
it is unlikely that 不大可能
But for that reason it is unlikely that the Chinese will follow up on this particular threat.
但正是由于这个原因,中国不大可能会将这个特别的威胁落到实处 。