Thirty years have now passed since the Voyager 1 spacecraft
snapped one of the most iconic and memorable pictures in spaceflight history. Known
as the “Pale Blue Dot,” the heart-rending view shows planet Earth as a single,

Thirty years have now passed since the Voyager 1 spacecraft
snapped one of the most iconic and memorable pictures in spaceflight history. Known
as the “Pale Blue Dot,” the heart-rending view shows planet Earth as a single,
bright blue pixel in the vastness of space, as seen from the outer reaches of
the solar system.
Now, NASA and the Jet Propulsion Laboratory have provided a
new and improved version, using state of the art image-processing software and
techniques to reprocess the thirty-year-old image. JPL software engineer and
image processor Kevin Gill, whose images we feature often on Universe Today,
led the effort.
In the past few decades, there has been an explosion in the number of extra-solar planets that have been discovered. As of April 1st, 2018, a total of 3,758 exoplanets have been confirmed in 2,808 systems, with 627 systems having more than one planet. In addition to expanding our knowledge of the Universe, the purpose of this search has been to find evidence of life beyond our Solar System.
In the course of looking for habitable planets, astronomers have used Earth as a guiding example. But would we recognize a truly “Earth-like” planet if we saw one? This question was addressed in a recent paper by two professors, one of whom is an exoplanet-hunter and the other, an Earth science and astrobiology expert. Together, they consider what advances (past and future) will be key to the search for Earth 2.0.
The paper, titled “Earth as an Exoplanet“, recently appeared online. The study was conducted by Tyler D. Robinson, a former NASA Postdoctoral Fellow and an assistant professor from Northern Arizona University, and Christopher T. Reinhard – an assistant professor from the Georgia Institute of Technology’s School of of Earth and Atmospheric Studies.
For the sake of their study, Robinson and Reinhard focus on how the hunt for habitable and inhabited planets beyond our Solar System commonly focuses on Earth analogs. This is to be expected, since Earth is the only planet that we know of that can support life. As Professor Robinson told Universe Today via email:
“Earth is – currently! – our only example of a habitable and an inhabited world. Thus, when someone asks, “What will a habitable exoplanet look like?” or “What will a life-bearing exoplanet look like?”, our best option is to point to Earth and say, “Maybe it will look a lot like this.” While many studies have hypothesized other habitable planets (e.g., water-covered super-Earths), our leading example of a fully-functioning habitable planet will always be Earth.”
The authors therefore consider how observations made by spacecraft of the Solar System have led to the development of approaches for detecting signatures of habitability and life on other worlds. These include the Pioneer 10 and 11 missions and Voyager 1 and 2 spacecraft, which conducted flybys of many Solar System bodies during the 1970s.
These missions, which conducted studies on the planets and moons of the Solar System using photometry and spectroscopy allowed scientists to learn a great deal about these bodies’ atmospheric chemistry and composition, as well as meteorlogical patterns and chemistry. Subsequent missions have added to this by revealing key details about the surface details and geological evolution of the Solar planets and moons.
In addition, the Galileo probe conducted flybys of Earth in December of 1990 and 1992, which provided planetary scientists with the first opportunity to analyze our planet using the same tools and techniques that had previously been applied throughout the Solar System. It was also the Voyager 1 probe that took a distant image of Earth, which Carl Sagan referred to as the “Pale Blue Dot” photo.
However, they also note that Earth’s atmosphere and surface environment has evolved considerably over the past 4.5 billion years ago. In fact, according to various atmospheric and geological models, Earth has resembled many environments in the past that would be considered quite “alien” by today’s standards. These include Earth’s many ice ages and the earliest epochs, when Earth’s primordial atmosphere was the product of volcanic outgassing.
As Professor Robinson explained, this presents some complications when it comes to finding other examples of “Pale Blue Dots”:
“The key complication is being careful to not fall into the trap of thinking that Earth has always appeared the way it does today. So, our planet actually presents a huge array of options for what a habitable and/or inhabited planet might look like.”
In other words, our hunt for Earth analogs could reveal a plethora of worlds which are “Earth-like”, in the sense that they resemble a previous (or future) geological period of Earth. These include “Snowball Earth’s”, which would be covered by glacial sheets (bu