The Arecibo Message: Humanity’s Greeting to the Cosmos

To this day, one of humanity’s most loaded questions remains unanswered: are we alone in this universe? Though we have yet to detect the presence of any extraterrestrial civilizations, that has not stopped humanity from attempting to make contact with whatever else might be out there.

Globular Cluster Messier 13. Image Source: Wikipedia

The most famous attempt to communicate humanity’s existence to the cosmos was a 3-minute binary transmission made in 1974 from Puerto Rico, a United States territory in the Caribbean. The broadcast was made using a planetary radar transmitter on the Arecibo radio telescope, and it was directed towards a globular cluster called Messier 13 (M13). The cluster contains about a third of a million stars, and the message’s senders hoped that an interstellar civilization ready to accept our transmission might be among these many star systems. However, M13 is near the edge of the Milky Way and lies at a whopping distance of about 25,000 light years. This means that it will take around 25,000 years for our message to actually reach the cluster, never mind the time it might take for us to actually receive a reply.

The Arecibo message encoded. Image Source: SETI Institute

The Arecibo message was the most powerful transmission ever purposefully beamed into space; it was equivalent in strength to a 20 trillion watt broadcast in all directions. The message includes 1679 bits that are meant to be arranged into a rectangular grid of 73 rows and 23 columns. These numbers were chosen because they are both prime, and presumbably, the extraterrestrials would recognize the significance. Once the aliens deciphered the message, they would have discovered the above image (though it carried no color information). Among other things, the picture represents DNA structure, a human stick figure, our solar system, the Arecibo radio dish, and eight biochemicals that define life on Earth.

Though the chances of receiving a reply to the Arecibo message are very slim, the project allowed us to more fully understand the complexities of communicating across time, space, and cultures.

Extrasolar Planets: A Search to Span Solar Systems

Recently, I have started work as an undergraduate research assistant in the Physics and Astronomy department at my university. The project I was assigned to is of a stellar nature; we are attempting to find evidence of extrasolar planets, or planets around other stars. Though we haven’t found any planets yet, I keep thinking about how crucial this type of work is to the future of the human race. Around 4,000 extrasolar planets have been confirmed by NASA, and it is amazing to think that one of these could be humanity’s next home. In this blog post, I will discuss the major approaches that astronomers use to detect planets outside of our solar system.

The Astrometric Method: Using the astrometric method, we can detect extrasolar planets by carefully monitoring small changes in the host star’s position in the sky. Planets orbit their host stars because of the enormous amount of gravitational force exerted on them by their stars. However, the laws of physics tell us that the planets also exert an equal amount of gravitational force on their host star. Though the star is much more massive, the planets can cause a star to “wobble” as it is gravitationally tugged at. Very few extrasolar planets have been identified using this method; the star studied must be relatively near to us, and observing positional changes may require long periods of observation.

Image Source: Wikipedia

The Doppler Method: Like the astrometric method, the Doppler method relies on the gravitational interactions and “tugs” between a host star and its planets. When a star is moving towards or away from us, we say that its light spectrum is blueshifted or redshifted, respectively. Alternating blueshifts and redshifts relative to average Doppler Shift can indicate a star’s motion or “wobble” due to its interactions with a planet or planets. The Doppler method has discovered many more extrasolar planets than the astrometric method, but it certainly does not come without its limitations. This technique is best suited for massive planets with close orbits, and because it calls for stellar spectra, large telescopes and long periods of observation are a must.

Image Source: EarthSky

The Transit Method: When an extrasolar planet’s orbital plane is situated along our line of sight, the planet will appear to travel in front of its star once every orbit. Astronomers call this a transit event. Similarly, half an orbit later, the planet will become eclipsed by its host star as it passes behind. We can detect these events by monitoring changes in the star system’s brightness. During a transit event, the star undergoes a characteristic dip in brightness as the planet blocks some of its light. During an eclipse, there is a dip in the system’s infrared brightness as the star blocks the infrared light emanating from the planet. Most extrasolar planets have been discovered using this method, but it is only feasible for planets with orbital paths that are oriented in just the right way.

Image Source: National Aeronautics and Space Administration

Direct Detection: This technique involves acquiring images or spectra of the planet. In theory, this is the best way to learn about an extrasolar planet; however, our current technology can only produce images with low resolution. There are other obstacles to directly detecting planets as well. For one, stars give off much more light than any planets that might be orbiting them. Because of diffraction, our telescopes also blur star light. Most extrasolar planets are too close to their bright host stars to be imaged directly from our vantage point, light years away. Second, compared to massive stars and the colossal distances between them, planets are miniscule.

An infrared image of a brown dwarf and an extrasolar planet (bottom left corner) located about 230 light years from Earth. Image Source: Slate