No visa required for Jordan. If you want to see Petra you can walk from the ship at Aqaba into town, get a hired car with a driver my wife and I saved £63 from not going on the ships tour, By the way I worked all over Jordan for 5 ½ years.
I would suggest that to be certain you ask your cruise agent to ascertain this for you or if you booked direct then ask Silversea. Sorry but their are very few of us who could give you a definite answer. By the way we love Silver Whisper, you are going to have such a great time on her .... Neil.
We have been twice to Jordan on cruise ships (not Silversea though)and both times the cruise company organised all visas.
Your agent should advise you about this, but it would be sensible to organise this your self to ensure you have all the correct documents. Enjoy the Silver Whisper you have booked the best!!!