It's important to really see the size of our galaxy (the Milky Way), its rotation, and also details about the edge of our Solar System. IMO the idea of extra-terrestrial visitation to earth just trivialises the scale of the problems of interstellar travel, not just in terms of time involved, but fuel load, and preservation of any on-board humanoid lifeforms.
The Milky Way
1. The Milky Way is a barred spiral galaxy with an estimated visible
diameter of 1.9 million light-years. It is estimated to contain 100–400 billion stars and at least that number of planets. There is suspected to be a dark matter halo around the Milky Way which may span as much as 2 million light years.
2. The Milky Way rotates with a rotational period of about 240 million years at the radius of our Solar System. The Milky Way as a whole, as well as rotating, is also moving at a velocity of approximately 600 km per second through the universe with respect to extragalactic frames of reference.
3. Our Solar System (marked Sun in image below) is located at a radius of about 27,000 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust.
Our Solar System
1. Aristarchus of Samos (c. 310 – c. 230 BC) presented the first known heliocentric model that placed the Sun at the center of the known universe (at the time) with the Earth revolving around it. [note that "helio" is Greek for "sun", so e.g. heliocentric means having the sun as the centre]
2. Aristarchus was influenced by Philolaus of Croton, but Aristarchus identified the "central fire" with the Sun, and he put the other planets in their correct order of distance around the Sun. 100 years earlier, Anaxagoras said that the stars were just other bodies like the Sun, albeit farther away from Earth.
3. Eratosthenes of Cyrene (c. 276 BC– c. 194 BC) was a Greek mathematician, geographer, and astronomer, and is best known for being the first person to calculate the circumference of the Earth, his calculation was very accurate.
4. Astronomical Units [AU] (150,000,000 km; 93,000,000 mi) are used to represent distances within our Solar System.
1 AU is the distance from Earth to the Sun.
5. The Sun's mass is 1.9885×10
30 kg,
it contains 99.86% of our Solar System's known mass, and dominates our solar system gravitationally.
6. The heliosphere is a vast, bubble-like region of space created by the Sun. In plasma physics terms, it is a cavity formed by the Sun in the surrounding interstellar medium. The "bubble" of the heliosphere is continuously "inflated" by plasma originating from the Sun, known as the solar wind.
7. Outside the heliosphere, this solar plasma gives way to the interstellar plasma permeating the Milky Way. Radiation levels inside and outside the heliosphere differ; in particular, the galactic cosmic rays are less abundant inside the heliosphere, so that the planets inside (including Earth) are partly shielded from their impact
8. Due to the fact that the Solar System is travelling through space, the heliosphere is not spherical and has a "bow wave" as shown in the image below
9. Voyager 2 was launched in August 1977, flew past Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. The probe left the heliosphere for interstellar space at 119 AU on 5 November 2018. It is not headed toward any particular star, although if undisturbed for 296,000 years, it should pass by the star Sirius at a distance of 4.3 light-years.
10. Voyager 1 was launched in September 1977, flew past Jupiter in 1979 and Saturn in 1980, making a special close approach to Saturn's moon Titan. The probe passed the heliopause at 121 AU on 25 August 2012 to enter interstellar space. It is headed towards an encounter with star AC +79 3888, which lies 17.6 light-years from Earth, in about 40,000 years.
11. Note that the initial speed required to escape the Sun from its surface would be 618 km/s (1,380,000 mph), dropping to to 42.1 km/s (94,000 mph) at Earth's distance from the Sun (1 AU), and 4.21 km/s (9,400 mph) at a distance of 100 AU. Note also that both Voyagers are still active, but are expected to become "derelict" in 2025. The speeds and current distances of both Voyagers are illustrated below. Both have been travelling ~15 km/s for the last 30 years. Voyager 1 is ~180 AU from the Sun, Voyager 2 is ~160 AU from the Sun.
Inference
When you take all of the above into account, using the technologies that are currently known, it seems completely implausible for aliens to reach our Solar System, land on earth, and then take off again and then leave our Solar System.
If we were to send a probe to a nearby star, in order to reduce the travel time, the probe would have to carry fuel to continually accelerate (using e.g. ion drive). But at half-way point it would then need to rotate by 180 degrees so that the thrust was used to start to continually decelerate the probe, else it would just fly right through the target star's planetary system at tremendous velocity and be impossible to enter orbit round the target star. Furthermore, if a craft carried humanoid lifeforms on board, they would be continually irradiated by the interstellar plasma in the Milky Way.
The only other way would be some technology that we are not aware of e.g. "anti-gravity" but that is a non-starter (does not exist, more to come soon, ish).