Let's say an alien species discovered Earth and wants to land here and establish contact, however their homeworld's gravity is only 46 percent of Earth's, Would it be possible for them to be able to walk on Earth? Is it possible for them to adapt to Earth's gravity? They are 1-2 ft tall and walk on two legs. Weighing about 50-60 pounds on their homeworld.
Short answer: it depends. The anatomy and physiology of your aliens will determine a lot.
For instance, their hearts are going to be working much harder to pump blood around their bodies, particularly when pumping upwards. Compare aliens which look like a 2 foot tall dog and aliens which look like a 2 foot tall ostrich or giraffe. The vertical distance between heart and brain in the ostrich-aliens is much greater than the dog-aliens. So the ostrich-aliens' hearts will be under much more strain. Their hearts will be pounding away like they've just run up a flight of stairs, even when they are just sitting watching TV.
Similarly, skeletons come with safety factors built in. When those safety factors are exceeded, bones break. For instance in humans, the force your leg bones has to bear when standing still is equal to your body weight. When you walk, that force doubles. When you sprint or jump over things, it is higher still. However, your bones can take all these forces, plus a bit extra for the safety factor.
Your aliens have come to a gravity more than double their own. So standing still will be the equivalent of walking, walking will be like jogging, jogging will be like running an Olympic hurdles race, and so on.
If their species has evolved to bounce around like gazelles (huge leaps, gaits called stotting and pronking), or is like a monkey species which habitually hurls itself out of trees onto the ground (as opposed to climbing down or jumping tree to tree) then their bones will be designed to take a pounding and have HUGE safety factors. So they may still be able to walk and jog, but should avoid running and jumping. If their ancestors evolved a more 'normal' lifestyle - zebra rather than a gazelle, or a normal monkey rather than a 'parkour' monkey - then walking may be the limit of what they can do without breaking bones, getting sprains and strains, etc.
Consider the elephant. Zoos have concrete moats round the elephant enclosure, because elephants are at the limits of the safety factors their bones can take. Elephants can't jump over that moat - they'd break their legs. In fact, elephants can't even run or trot, because their leg bones can't take it. A charging elephant is speed walking!
EDIT TO ADD EXAMPLES: at 1g a horse can walk, trot, gallop and jump over fences. The much heavier rhino can walk, trot and gallop but not jump over fences. The Elephant can only walk (partly weight and partly due to not having bones as thick as it 'should' for an animal that heavy - i.e. reduced safety factors). So your aliens may be 'horses' on their homeworld, but 'rhinos' or - if they are really unlucky - 'elephants' on earth.
Your aliens muscles will slowly get stronger as they adapt to the gravity. They may lay down some more bone to reinforce their skeleton. But the bone they'll be making is more of the same 'low gravity' bone with low gravity safety factors. Evolution won't have given them the tools to make 1g bone.
There will also be a lot of wear and tear on soft tissues. Knee cartilages will be feeling the strain, spine compressing on disks, sole of the foot taking a pounding, and so on. They may spend all their time with bad backs and aching feet.
Walking for the low-gravity aliens would be like running a marathon. This is something that is best done in small doses.
While exosuits are feasible. An alternative is mobile flotation tanks. The aliens will wear a protective suit, and rest inside the mobile tanks in a floating position. With medical equipment in case of "gravity stress" problems and possibly cardiovascular apparatus to take the load off their bodies.
One aspect about low-gravity aliens visiting Earth is the fact that their spacecraft, when they land and take-off from planet Earth, will have to be at relatively low acceleration, compared to the kind of rocket take-offs we know, and be for a much longer duration. Unless their ships are propelled by a super-advanced field-drives which either neutralises or considerably reduces the g-forces accompanying the acceleration.
If their bone structure can withstand the stress, then they can, but it will be exhausting and highly uncomfortable. For comparison, imagine carrying around your own body weight in extra weight all day and night, evenly distributed over your body. Every step will be a chore, lifting your arms and even your head will feel like workout, every breath you take is a struggle. Not even lying down is much comfort because you will be pulled down so hard.
You will want only your most able-bodied aliens to ever visit Earth, and even they will require some sort of mechanical exosuit or strength-boosting medication to get through the day without too many problems.
If the aliens have arrived via a long spaceship journey, and if they knew what was waiting for them when the got here, then they would have been well advised to use the journey as preparation.
Their spaceship should have some kind of artificial gravity. Whether by some high tech plating (per Star Trek) or simply the craft revolving (per Space Oddesey), the strength of this gravity could be increased steadily through the journey time to help the travellers adjust to the conditions at the destination planet. A regime of weight training and exercise en route would be necessary as well.
Picking suitably strong individuals for the journey in the first place would also be a consideration of course. Weaker individuals would struggle to adapt, but for stronger individuals coming off the ship after a journey helping them to adapt, they should be in good shape to cope with conditions on Earth.
There is one other caveat to mention though. Breathing.
If the aliens' planet has a lower gravity, then it follows that it also has a significantly lower atmospheric pressure. Even if their air composition is similar to ours, breathing air on Earth may cause them to hyperventilate. They will therefore likely need assisted breathing aparatus of some kind. This will appreciably add to the weight that they need to carry with them, which in turn will make adapting to the increased gravity a bit harder still.
That is how the aliens experience Earth.
Assuming they are otherwise made of flesh similar to ourselves, this should be difficult but not nearly impossible.
However, you also have them at only 1-2 ft tall.
There are two factors that make high gravity a problem.
- everything weighs more, thus needs more muscle power to move effectively.
and much much more important.
- your heart has to pump blood up against the gravity, and your feet need to resist the static pressure of supporting a column of blood as tall as you are. These vascular issues are the main problem with higher (and lower) gravity.
For your aliens, this second factor is GREATLY diminished, because they are so short!
In all, in my opinion but supported at least a bit by facts, your aliens will be fully mobile just tiring much quicker than normal. They will also tend to be clumsy, as they fall over following an imbalance more than twice as fast.
The problem of STAIRS!
If your biped aliens are proportioned anything like humans:
To a 1-2ft tall, biped, operating in a 2.2g (for them) environment, normal stairs will be IMPOSSIBLE to climb! Even a normal sidewalk with a vertical riser of 6 inches will be a WALL somewhere between knee height and navel height to them. You try climbing a wall that high, while in 2.2g gravity
And at 2feet tall, weighing 60lb on their home planet, they will weigh 132lb here. That makes for a very short, squat, heavy little alien! Not agile climbers by any concept.