美国有线新闻 CNN 2016成地中海难民最悲催的一年 太空飞行对宇航员造成伤害（在线收听）

The United Nations refugee agency says this year has been the worst ever for migrants and refugees crossing the Mediterranean Sea into Europe.

Despite the fact that far fewer migrants are trying to cross than the number who did in 2015, many more had died this year — at least 3,800 people so far or one in every 88 trying to make the crossing. Compare that with one death for every 269 people last year.

The journey is even more dangerous for those migrants trying to reach Europe from Libya. The North African country is in chaos. It has no central government, but it does have a number of smuggling networks and many of them use flimsy rafts or boats that aren't really seaworthy.

They're often overcrowded with refugees and migrants and sent over the central Mediterranean, facing strong currents, bad weather and odds increasingly stuck against a safe journey.

Next today, new research suggests space travel can be a real pain in the back. Since missions got longer in the late 1980s, more than half of the U.S. astronauts who'd spent time in space had complained of back pain. And it didn't get better when they got back to earth.

A new study funded by NASA says the problem is a major weakening of the muscles of the lower back. Researchers say in space, astronauts aren't bending forward or using their lower backs to move. That led to a 19 percent decrease in muscle tone during a trip to the International Space Station.

And even after six weeks of training when they came back home, the muscles still hadn't fully recovered. Doctors say yoga and core training could help. They're concerned because the muscle loss they saw was on astronauts who'd been in space for four to seven months. It could take nine months to go to Mars. And that planet's gravity is weaker than Earth's is.

Health problems in space go beyond back pain.

REPORTER: The space station has multiple science labs where astronauts spend most of their time. Without gravity, endless new research possibilities are opened up.

UNIDENTIFIED MALE: Every part of your day, you're jumping from one experiment to the other. We were doing flame research almost every day and then a lot of fluid research to see what's going on with fluid dynamics up in zero g.

REPORTER: And this weightless environment is the perfect place to examine how the human body reacts to space, bringing NASA closer to their chief objective of sending people to Mars.

UNIDENTIFIED MALE: Another huge chunk is what's going on with our bodies while we're up there? So, you take away gravity. Right now, we're standing here, we're leaning up our hips. We're leaning up our leg muscles. And when you get up to that zero gravity situation, all of that goes away.

The first thing your body wants to do, you're not using those muscles, let's get rid of them. You don't need that bone to be that strong, let's get rid of that, and start weakening it down. Astronauts have vision changes when they're up in space. So, the fluid shifts and it's actually pressing on the back of your eyes. So, every two to three weeks, we're doing in-depth look at our eyes.

There was really no part of the human body that was not studied in depth the whole time you're up there.

If we're ever going to spend 500 days going off to Mars, we need to know exactly what's going on with the human body.

REPORTER: In order to counteract some of the health risks, astronauts spend an average of two and a half hours a day exercising on station.

Being in space is certainly no vacation. But up there, nothing is mundane.