Former Nest CEO Tony Fadell. Kimberly White / Getty There's been a mini exodus of sorts among executives at Google's parent company, Alphabet.

Alphabet, which formed last year as a conglomerate of separate companies, is designed to help the company find the next big thing outside of Google's core advertising and search businesses.

But within a year of Alphabet's formation, there have been several shake-ups and departures at the top of these divisions, especially since this summer.

The challenge for these companies and their leaders is to prove to Alphabet's CEO, Larry Page, and CFO, Ruth Porat, that they can turn into growing businesses.

While Alphabet doesn't report financials for these "other bets," the recent departures are our best hint that some divisions have struggled or their leaders aren't thrilled with the new pressure now that they're no longer hiding under Google's umbrella.

Here's a breakdown of the most important Alphabet executive departures so far this year:

Tony Fadell, Nest

The highest-profile departure was Tony Fadell, the former Apple executive and CEO of Nest, Alphabet's smart home appliance company that makes connected thermostats and cameras. Fadell stepped down as Nest's CEO in June following reports of inner turmoil in the company and a damning blog post by Greg Duffy, the former head of Nest's camera business.

Fadell gave a particularly rough interview to The Information before his departure in which he tersely defended his management style. He was out shortly after that.

Fadell is still an adviser at Nest.

Bill Maris, GV

Bill Maris. Getty / Noam Galai

Bill Maris was the head of GV, formerly known as Google Ventures, an Alphabet company that invests in early-stage startups. Maris founded GV in 2009 and left in August after some other members of his team left the company.

Craig Barratt, Google Fiber

Craig Barratt was the CEO of Google Fiber, the internet service provider that offered super-high-speed broadband in select cities. Barratt stepped down as CEO on Wednesday and announced the company had stopped plans to expand its service to more cities. Instead, it will focus on new ways to deliver internet through wireless technologies.

Barratt is now an adviser at Google Fiber.

Dave Vos, Project Wing

Dave Vos was the head of Project Wing, a division of X, Alphabet's "moonshot" lab that works on a bunch of crazy, futuristic projects. Project Wing experimented with delivery drones and even ran a pilot program to deliver Chipotle burritos to students at Virginia Tech.

Vos stepped down from Project Wing earlier this month.

Chris Urmson, self-driving cars

Chris Urmson. Medium / Chris Urmson

Chris Urmson, the tech lead for X's self-driving car project, left the company in August. He had worked on the project for seven years.

Do you know anything about what's happening at Alphabet? Shoot me a note at skovach@businessinsider.com. I'm discreet!